Reference Dennis' first graph: The number of cycles (lifespan) on the vertical axis versus Depth of Discharge (DoD) is amazing, especially when compared to other battery chemistries..
I'm curious to how that chart was developed. Repeatedly discharging a lithium-based cell down to 80% DoD for 10,000 cycles seems no easy feat and time-consuming; similarly down to 20% for a whopping 100,000 cycles.
I'm also curious as what rate of discharge and charge was used. What rate of charge/discharge is optimal, and what is "good enough for our application."
And what about temperature? Other than the low-temperature and high-temperature cut-off provided by many BMS, is there any benefit to charge rate adjustment for battery temperature between, say, 40°F and 100°F?
I understood absolutely nothing in this article. Please remember you aren't speaking to other electricians when publishing articles. Do I charge over 80 % or not ? Do I recharge when at 20% ?
The graph in the article tells us that LFP batteries will last much longer if we recharge them before they are fully discharged and the less discharged they are, the better. I didn’t see anything about what state of charge they should be charged to but data in the graph implies charging to 100% SoC. As was said, there is general rule of thumb “out there” that avoiding charging above 80% and discharging below 20% is a strategy to make your battery last longer. Said differently, charging above 80% and discharging below 20% only when you have to is a strategy that to extend battery life. What we can’t tell from this article is whether an 80/20 strategy is better or worse than an 100/40 strategy but the graph suggests that both are better than 100/0.
My discussion with several Lithium battery manufacturers suggests that 100/20% is the most practical charging protocol. I’ll see if I can get my contacts at Lion Energy or Battle Born to do an Ask the Expert video webinar with me.
That would be great! I’ve also read that leaving a LFP battery at 100% SoC is not good for it but would love to hear what one of the battery manufacturers thinks.
It depends somewhat on the battery chemistry. I have been building Li battery systems since 2013. Some of the Li-ion battery systems we built using LFP cells are used in float service as back up power for communications sites. With a CV of 14.2 Volts, these systems are operating for over 7 years.
We recommend our batteries (LiFeBlue) be fully charged regularly, at least weekly. One reason is to maintain cell balance. Our balance circuit turns on at 3.5V. That's about 14 Volts on the battery pack. If you are not fully charging, you will rarely reach that voltage. Our CPU algorithms also use full charge for calculating things like SoC, remaining capacity, battery health, battery capacity, and battery cycles. Most of our sales are to RV and marine customers. Following that "rule of thumb" is not good for our batteries. Most people that have issues have been deficit charging them for years. Bottom line, follow the manufacturer instructions.
Great info, thanks Larry! Your point about the need to recharge periodically to 100% to get the BMS to rebalance the cells is a great one! The more one learns about Lithium batteries, the more questions that one can ask!
Yes, I remember reading about Lithium cell balancing issues a few years ago, but I didn’t think about requiring a high enough charging voltage periodically to make it work properly.
Using only three quarters of your battery gives you 10k cycles. If you did that every day of the year, your battery will last 27 years, according to the chart. Who uses that much battery every day? Even if you did, I think by then you will be using different batteries (and connected equipment) anyway. So I wouldn’t worry about it! ;)
That being said, I wonder why the graph stops at 95%. Is 100% where the battery turns off (usually near rated capacity), or at total physical depletion?
Does it really matter with LiFePO4 cells, even with 100% dod, it looks like 1500 cycles compared to 3-400 cycles on lead acid. The 2-3X higher capacity of LiFePo4 in the same size as Lead Acid in typical RV you never need to go below 50%. Its easy to get buried in numbers (I'm retire Electrical Engineer)
Excellent article. There is so much misinformation in the RV lithium battery world I found it refreshing to read information regarding lithium batteries we use as replacements or substitutions for lead-acid batteries. While lead-acid batteries do not have a BMS to protect them from unrecoverable damage, most RV lithium batteries share similar properties regarding depth of discharge and battery life. Yet, most users of RV lithium batteries will likely replace them due to age rather than deep discharges. As age is also the reason I replace my lead-acid batteries.
That answers nothing usable related to the question. I appreciate the general information about the LiFePO4 and LiPO, butgtuis didn’t answer the question.
For him specifically, was the advice of his son accurate? Depth of discharge related to strain placed on battery and therefore lifecycle. But at what point does it become a significant determinant of battery life? Is it below 20%, 10%, 5% or when the BMS shuts down the battery? And for charging, same question. And if you could answer that question for both LiFePO4 and LiPO that would be great. Just a general guideline is all any of us could really ask for.
My RV house batteries and my power station are both LiFePO4 but I also wonder about my Apple products which are LiPO. I try to keep the LiPOs between 20 and 90%. But often they make it to 100% if I leave them to just charge even though I’ve read where Apple says 100% has no detrimental effect, but various “experts” online say the 20/80 rule. Heck, some say to do a full discharge and recharge (0-100%) once a month to maintain capacity. No I don’t do that. That reminds me of NiMH battery advice
Please note that this article has an Intermediate Difficulty warning sign at the top, which is why there’s engineering speak. I’ll do an Easy Difficulty version in a few days once I get confirmation from my Lithium battery manufacturers. This is an important question to answer. 😁
Reference Dennis' first graph: The number of cycles (lifespan) on the vertical axis versus Depth of Discharge (DoD) is amazing, especially when compared to other battery chemistries..
I'm curious to how that chart was developed. Repeatedly discharging a lithium-based cell down to 80% DoD for 10,000 cycles seems no easy feat and time-consuming; similarly down to 20% for a whopping 100,000 cycles.
I'm also curious as what rate of discharge and charge was used. What rate of charge/discharge is optimal, and what is "good enough for our application."
And what about temperature? Other than the low-temperature and high-temperature cut-off provided by many BMS, is there any benefit to charge rate adjustment for battery temperature between, say, 40°F and 100°F?
I understood absolutely nothing in this article. Please remember you aren't speaking to other electricians when publishing articles. Do I charge over 80 % or not ? Do I recharge when at 20% ?
I will translate the engineering speak tomorrow.
The graph in the article tells us that LFP batteries will last much longer if we recharge them before they are fully discharged and the less discharged they are, the better. I didn’t see anything about what state of charge they should be charged to but data in the graph implies charging to 100% SoC. As was said, there is general rule of thumb “out there” that avoiding charging above 80% and discharging below 20% is a strategy to make your battery last longer. Said differently, charging above 80% and discharging below 20% only when you have to is a strategy that to extend battery life. What we can’t tell from this article is whether an 80/20 strategy is better or worse than an 100/40 strategy but the graph suggests that both are better than 100/0.
My discussion with several Lithium battery manufacturers suggests that 100/20% is the most practical charging protocol. I’ll see if I can get my contacts at Lion Energy or Battle Born to do an Ask the Expert video webinar with me.
That would be great! I’ve also read that leaving a LFP battery at 100% SoC is not good for it but would love to hear what one of the battery manufacturers thinks.
Yes! Please tell us what the folks at battleborn are saying!
I’m sending an inquiry to my engineering contacts at BattleBorn, Renogy and Lion Energy. That should give us some useful DoD lifespan data.
Hi Doug,
It depends somewhat on the battery chemistry. I have been building Li battery systems since 2013. Some of the Li-ion battery systems we built using LFP cells are used in float service as back up power for communications sites. With a CV of 14.2 Volts, these systems are operating for over 7 years.
We recommend our batteries (LiFeBlue) be fully charged regularly, at least weekly. One reason is to maintain cell balance. Our balance circuit turns on at 3.5V. That's about 14 Volts on the battery pack. If you are not fully charging, you will rarely reach that voltage. Our CPU algorithms also use full charge for calculating things like SoC, remaining capacity, battery health, battery capacity, and battery cycles. Most of our sales are to RV and marine customers. Following that "rule of thumb" is not good for our batteries. Most people that have issues have been deficit charging them for years. Bottom line, follow the manufacturer instructions.
Larry Crutcher, GM
LiFeBlue Battery
(920) LiFePO4
(920) 543-3764
Great info, thanks Larry! Your point about the need to recharge periodically to 100% to get the BMS to rebalance the cells is a great one! The more one learns about Lithium batteries, the more questions that one can ask!
Yes, I remember reading about Lithium cell balancing issues a few years ago, but I didn’t think about requiring a high enough charging voltage periodically to make it work properly.
Using only three quarters of your battery gives you 10k cycles. If you did that every day of the year, your battery will last 27 years, according to the chart. Who uses that much battery every day? Even if you did, I think by then you will be using different batteries (and connected equipment) anyway. So I wouldn’t worry about it! ;)
That being said, I wonder why the graph stops at 95%. Is 100% where the battery turns off (usually near rated capacity), or at total physical depletion?
Does it really matter with LiFePO4 cells, even with 100% dod, it looks like 1500 cycles compared to 3-400 cycles on lead acid. The 2-3X higher capacity of LiFePo4 in the same size as Lead Acid in typical RV you never need to go below 50%. Its easy to get buried in numbers (I'm retire Electrical Engineer)
Excellent article. There is so much misinformation in the RV lithium battery world I found it refreshing to read information regarding lithium batteries we use as replacements or substitutions for lead-acid batteries. While lead-acid batteries do not have a BMS to protect them from unrecoverable damage, most RV lithium batteries share similar properties regarding depth of discharge and battery life. Yet, most users of RV lithium batteries will likely replace them due to age rather than deep discharges. As age is also the reason I replace my lead-acid batteries.
That answers nothing usable related to the question. I appreciate the general information about the LiFePO4 and LiPO, butgtuis didn’t answer the question.
For him specifically, was the advice of his son accurate? Depth of discharge related to strain placed on battery and therefore lifecycle. But at what point does it become a significant determinant of battery life? Is it below 20%, 10%, 5% or when the BMS shuts down the battery? And for charging, same question. And if you could answer that question for both LiFePO4 and LiPO that would be great. Just a general guideline is all any of us could really ask for.
My RV house batteries and my power station are both LiFePO4 but I also wonder about my Apple products which are LiPO. I try to keep the LiPOs between 20 and 90%. But often they make it to 100% if I leave them to just charge even though I’ve read where Apple says 100% has no detrimental effect, but various “experts” online say the 20/80 rule. Heck, some say to do a full discharge and recharge (0-100%) once a month to maintain capacity. No I don’t do that. That reminds me of NiMH battery advice
Please note that this article has an Intermediate Difficulty warning sign at the top, which is why there’s engineering speak. I’ll do an Easy Difficulty version in a few days once I get confirmation from my Lithium battery manufacturers. This is an important question to answer. 😁