Hello,I'm about to move into a conversion van full-time, 80% boondocking, and would like your advice about what I'm planning. My electrical requirements won't be much. I don't expect to use more than 400 AC watts or it's DC equivalent at any one time, and normal usage will be less than 200 AC watts or it's DC equivalent for 9 hours a day. Currently I have 2 x 100w flexible solar panels and a 600w pure sine inverter.I'm planning on getting a 100ah lithium (LiFePO4) battery ( https://battlebornbatteries.com/shop/12v-lifepo4-deep-cycle-battery/) and a solar MPPT charge controller for it (probably https://www.amazon.com/Victron-SmartSolar-Charge-Controller-Bluetooth/dp/B073ZJ3L13). A big reason that I'd like a lithium battery is because I will occasionally want to bring it with me to a friend's house to charge it from the wall, and 30 pounds in a backpack allows that.Here are my biggest questions: how will I know when the lithium battery is fully charged, and how will I know how much capacity is used or remaining? With lead batteries it's fairly simple because the volts indicate remaining capacity, but from my understanding, lithium's voltage doesn't change much between it's full and empty states (I could be wrong here).

chuck3 wrote:Here are my biggest questions: how will I know when the lithium battery is fully charged, and how will I know how much capacity is used or remaining? With lead batteries it's fairly simple because the volts indicate remaining capacity, but from my understanding, lithium's voltage doesn't change much between it's full and empty states (I could be wrong here).You need AH meter, a.k.a. battery monitor, not cheap ~$170 and it won't help when you take the battery away for charging. Even with flooded/led battery you can't effectively estimate the remaining charge by looking at the voltage, other than early morning with loads off and before solar starts. Ebay had some $40 re-settable AH meters, maybe somebody will provide a link.If not a monitor, then get LifeBlue Battery, it comes with Bluetooth monitoring, i.e. the "monitor" chip is mounted in the battery case. 2 pounds lighter than Battleborn 100AH. Can't say anything good or bad about either brand.

The manual for your battery says the bulk voltage is 14.2v-14.6v. When that drops it should be fully charged. I was surprised to see there's an absorb phase. Most Li's I've seen don't have that. I hope the battery is better quality than the grammar in that manual.As for what's used, you'll need an ah meter for that.

2oldman wrote: Actually, with mine there is quite a difference in its resting vs bulk/float voltage.Because when it drops to 13x, it is not charging anymore, basically the same as pulling the plug off.OTH, bulk charging is 14x. Bringing it all the way up to manufacture specked maximum is wrong, it is not supposed to be fully charged every time, but I won't go there now.

Back the envelope calculations suggest this:Not enough capacity.At a nominal 12 volts, 100 amp-hours is 1200 watt-hours.Your demand is 1800 watt hours per day.LI prefers to not be charged to 100%. Best life cycle is 20 to 90. That yields about 70 amp-hours or 840 watt-hours.The solar @ 200 watts is, best case, going to average 1000 watt-hours per day.Solution:Double the solar wattage or even triple it.Use AGM instead of the extremely pricey Battleborn jars.Talk to 2Oldman who has a working system using LI recharged from solar.

Almot wrote:...If not a monitor, then get LifeBlue Battery, it comes with Bluetooth monitoring, i.e. the "monitor" chip is mounted in the battery case. 2 pounds lighter than Battleborn 100AH. Can't say anything good or bad about either brand.Had an interesting conversation on another forum about charging the lifeblue batteries and their built-in SOC monitoring. Apparently you can get them upto 100% SOC according to their interior monitor, but still not be anywhere near the "absorption" V of 14.4-14.6V. In his case, the 300Ah battery bank kept sucking up 20A even at a nominal 100% SOC and V in the mid-high 13Vs. So now he manually terminates the charge when SOC reaches 100%. Not sure if I'm ready to trust these drop in replacement LiFePO4 batteries and their BMS just yet.Curious how 2oldman handles SOC.

Advice on Lithium Solar setup | Good Sam Community

Almot
Explorer III
Jan 26, 2018
2oldman wrote:
Actually, with mine there is quite a difference in its resting vs bulk/float voltage.

Because when it drops to 13x, it is not charging anymore, basically the same as pulling the plug off.

OTH, bulk charging is 14x. Bringing it all the way up to manufacture specked maximum is wrong, it is not supposed to be fully charged every time, but I won't go there now.
2oldman
Explorer II
Jan 26, 2018
The manual for your battery says the bulk voltage is 14.2v-14.6v. When that drops it should be fully charged.

I was surprised to see there's an absorb phase. Most Li's I've seen don't have that. I hope the battery is better quality than the grammar in that manual.

As for what's used, you'll need an ah meter for that.
Almot
Explorer III
Jan 26, 2018
chuck3 wrote:

Here are my biggest questions: how will I know when the lithium battery is fully charged, and how will I know how much capacity is used or remaining? With lead batteries it's fairly simple because the volts indicate remaining capacity, but from my understanding, lithium's voltage doesn't change much between it's full and empty states (I could be wrong here).

You need AH meter, a.k.a. battery monitor, not cheap ~$170 and it won't help when you take the battery away for charging. Even with flooded/led battery you can't effectively estimate the remaining charge by looking at the voltage, other than early morning with loads off and before solar starts.
Ebay had some $40 re-settable AH meters, maybe somebody will provide a link.

If not a monitor, then get LifeBlue Battery, it comes with Bluetooth monitoring, i.e. the "monitor" chip is mounted in the battery case. 2 pounds lighter than Battleborn 100AH. Can't say anything good or bad about either brand.

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