BattleBorn response to continually charging LiFePO4s

[xrated]

For us Lithium doesn't make sense. We don't boon dock a lot anymore which means we are always plugged in. We replaced our golf cart batteries last year with two more TL6 golf cart batteries. To change out now would make no sense. With the high cost of the batteries and having to replace the converter we would never see any improvement from what we have now. Who knows what we will be doing 8 years from now, but very likely we would not still be in the same trailer. I don't think I would ever know the difference so I will not go the the expense.

Gary, you are correct....LFP batteries are not for everyone, and at first glance, we would be in that same category of almost never boondocking and always being plugged in. The difference for me however, was two fold. 1st....my two Trojan T105s were getting old enough that they didn't hold a charge nearly as long as when they were new, so something was going to have to take their place. 2nd. We were going to have our Norcold 2118 converted over to a Twin Compressor 12VDC unit by J.C. Refrigeration and I knew that would require a hefty battery for long travel days. So in researching the LFP batteries, I decided to build my own and ended up with four 302AH cells and built a LFP battery from them. Then in May last year, we made the trip to Shipshewana, IN to JC Refrigeration and had the Norcold converted over to the Twin compressor 12VDC unit. I'm 100% happy with both the battery build AND the Norcold conversion and the fact that I have quite a lot more battery AH than I would have had with the two 6V GC batteries. I figure that if I take the fully charged LFP battery down to around 10% SOC, that will give me a little over 270AH from it. The two Trojan T105s with 230AH, but run down to the traditional 50% SOC comes out to 115 usable AH......so way more than double the usable AH from the LFP battery.

[Ynot4me2]

As it relates to liFePO4 what is a cycle? Every time it goes as mentioned above 100% to 0% back to 100% or the total of that % or anytime it gets a charge (regardless of the charge amount)? I've always wondered and never really ever found a clear answer. We're going liFePO4 for the RV as we need more ah and also could use less weight. I also wondered for our EV.

[MoonShadow_1911]

As it relates to liFePO4 what is a cycle? Every time it goes as mentioned above 100% to 0% back to 100% or the total of that % or anytime it gets a charge (regardless of the charge amount)? I've always wondered and never really ever found a clear answer. We're going liFePO4 for the RV as we need more ah and also could use less weight. I also wondered for our EV.

With DC circuits, which applies to batteries regardless of the type, a cycle is considered charge then discharge, capacitors have this cycle as well, so though they are usually in the hundreds of thousands to millions of cycles.

If one really wanted to make sure the battery bank lasted as long as possible, one would have to design and build a power management system that would charge the batteries to within 95% of capacity, then allow then to discharge to within 15% of depletion state, then to charge them again to within 95%.

Why 95%? This is to allow environmental condition changes that affect the charging cycles. If one wanted to charge fully to 100% and discharge to 5%, then the power management system would have to be designed and built specifically for the battery bank in use.

I could design either version, but the cost to design and build it would far outweigh the COTS items available now.

[A.Texas.Yankee]

As it relates to liFePO4 what is a cycle? Every time it goes as mentioned above 100% to 0% back to 100% or the total of that % or anytime it gets a charge (regardless of the charge amount)? I've always wondered and never really ever found a clear answer. We're going liFePO4 for the RV as we need more ah and also could use less weight. I also wondered for our EV.

See my post above.

[WhittleBurner]

Gary, you are correct....LFP batteries are not for everyone, and at first glance, we would be in that same category of almost never boondocking and always being plugged in. The difference for me however, was two fold. 1st....my two Trojan T105s were getting old enough that they didn't hold a charge nearly as long as when they were new, so something was going to have to take their place. 2nd. We were going to have our Norcold 2118 converted over to a Twin Compressor 12VDC unit by J.C. Refrigeration and I knew that would require a hefty battery for long travel days. So in researching the LFP batteries, I decided to build my own and ended up with four 302AH cells and built a LFP battery from them. Then in May last year, we made the trip to Shipshewana, IN to JC Refrigeration and had the Norcold converted over to the Twin compressor 12VDC unit. I'm 100% happy with both the battery build AND the Norcold conversion and the fact that I have quite a lot more battery AH than I would have had with the two 6V GC batteries. I figure that if I take the fully charged LFP battery down to around 10% SOC, that will give me a little over 270AH from it. The two Trojan T105s with 230AH, but run down to the traditional 50% SOC comes out to 115 usable AH......so way more than double the usable AH from the LFP battery.

I totally understand. We have been thinking about a new trailer. Which would mean 12 volt fridge. In that case we too would then go to Lithium.

[jkwilson]

As it relates to liFePO4 what is a cycle? Every time it goes as mentioned above 100% to 0% back to 100% or the total of that % or anytime it gets a charge (regardless of the charge amount)? I've always wondered and never really ever found a clear answer. We're going liFePO4 for the RV as we need more ah and also could use less weight. I also wondered for our EV.

Historically with batteries, saying a cycle, or cycle life without also specifying average depth of discharge had no meaning. You can bet in marketing materials when they brag about cycle life, they are talking minimum average depth of discharge.

Battery manufacturers have a chart which graphs cycle life vs. average depth of discharge. It can be very difficult to find such information for a specific battery. Trojan may be the only manufacturer I know of that makes it readily available.

But relatively recently with the advent of rechargeable devices like phones, it’s become common to refer to a cycle as the process of discharging and recharging 100% of the capacity of the battery. So if you discharge 25% every day for 4 days, you’ve used one cycle.

The newer method isn’t as simple as it seems though, because battery capacity decreases with use.

Neither method has a hard rule as to when the battery is at end of life. If I have a 100AH battery and I use an average of 70AH daily before recharging, the battery may no longer be able to supply that 70AH after just a few years. But if I bought a 200AH system with no change in usage, my average depth of discharge is cut in half, and the point at which the battery no longer has enough remaining capacity is delayed both by the reduced usage and the larger original capacity. The larger battery may have 3 or 4 times the cycle life as the smaller one in this scenario.

And you can’t go to the extreme and have a significantly oversized battery bank and expect it last forever as there are still age related factors that reduce the battery capacity over time regardless of use.

[jkwilson]

I worry about the technical advice when a company seems mystified by the guidance to not store a LiFePo battery at 100% state of charge. All such batteries suffer from corrosion of the current collector. It results in slow deterioration of the battery over time. Corrosion is a little worse near 0% and 100% state of charge.

During longer periods (months) of non-use, the aging rate is reduced by maintaining a moderate state of charge.

This corrosion is among the most studied challenges in these batteries and has not been solved by anyone. For a “manufacturer” to say they don’t know where the idea came from is simply bizarre.

[MoonShadow_1911]

Historically with batteries, saying a cycle, or cycle life without also specifying average depth of discharge had no meaning. You can bet in marketing materials when they brag about cycle life, they are talking minimum average depth of discharge.

Battery manufacturers have a chart which graphs cycle life vs. average depth of discharge. It can be very difficult to find such information for a specific battery. Trojan may be the only manufacturer I know of that makes it readily available.

But relatively recently with the advent of rechargeable devices like phones, it’s become common to refer to a cycle as the process of discharging and recharging 100% of the capacity of the battery. So if you discharge 25% every day for 4 days, you’ve used one cycle.

The newer method isn’t as simple as it seems though, because battery capacity decreases with use.

Neither method has a hard rule as to when the battery is at end of life. If I have a 100AH battery and I use an average of 70AH daily before recharging, the battery may no longer be able to supply that 70AH after just a few years. But if I bought a 200AH system with no change in usage, my average depth of discharge is cut in half, and the point at which the battery no longer has enough remaining capacity is delayed both by the reduced usage and the larger original capacity. The larger battery may have 3 or 4 times the cycle life as the smaller one in this scenario.

And you can’t go to the extreme and have a significantly oversized battery bank and expect it last forever as there are still age related factors that reduce the battery capacity over time regardless of use.

I tried to keep my response as non-technical as 3 could while trying to convey the technical information you just did. Thanks! [emoji106]

[xrated]

I worry about the technical advice when a company seems mystified by the guidance to not store a LiFePo battery at 100% state of charge. All such batteries suffer from corrosion of the current collector. It results in slow deterioration of the battery over time. Corrosion is a little worse near 0% and 100% state of charge.

During longer periods (months) of non-use, the aging rate is reduced by maintaining a moderate state of charge.

This corrosion is among the most studied challenges in these batteries and has not been solved by anyone. For a “manufacturer” to say they don’t know where the idea came from is simply bizarre.

John, I agree with that statement 110%. I even stated in an earlier post that BB's recommendation of long term storage at 100% SOC was basically a line of poop and I totally disagree with what they say. The marketers and lawyers rule....vs. common sense and electrical facts.

[ajg617]

John, I agree with that statement 110%. I even stated in an earlier post that BB's recommendation of long term storage at 100% SOC was basically a line of poop and I totally disagree with what they say. The marketers and lawyers rule....vs. common sense and electrical facts.

So it took two+ full days for BB to respond which I thought was on the longish side and the tone of the response was actually a little disappointing.