Battery Basics 101

[gcyeaw]

One thing I would suggest is taking measurements at the batteries and comparing that to what ever meter you are referencing in the coach to determine battery level. I believe (but could be wrong) the actual battery charge level is determined after a rest with no load. So you need to do some testing to get a handle on the in-coach meter and at-battery readings under the normal parasitic loads compared to the no load at rest battery readings.

All this does is help you better understand what is happening with your coach so you can manage your power usage to protect your batteries. It will also help in making a decision to go solar

Solar is not in the cards ($$) for me, but it would be nice.

[NoGas]

Solar is not for everyone. However, as panel prices have decreased it has become a cost effective option. If you understand how the Absorption charging phase works (see post #1 above) and regularly boondock without shorepower, it is easy to see why solar is an excellent way to get that last 10-15% back into your batteries without running a generator for hours and hours. Even if you install a solar array that is too small to charge your batteries without generator help, it's still good to have them. That's because you can efficiently use the generators high current output to quickly get the batteries back up to that 85% range, then shut it down and allow the sun to take over when the Absorption current required has tapered off. Using this technique your batteries would head into the night with a 100% SOC (making them last longer) and you'd significantly reduce generator run time (saving more $$) - a true win-win. Besides, where we go the sun shines almost every day .

[NoGas]

The RV Geeks just posted an hour long video of a presentation that covers pros and cons of the three battery types. Is a good stuff, especially if Q-13 was your first experience off-grid and you’ve decided to upgrade yours. Find it HERE.

https://youtu.be/PZ7HMRReZKY

[Kiwi3]

It is a good video. I have to say I'm thinking of doing my batteries first, then maybe adding more solar. I found these 3600 Watt Hour batteries from KiloVault. They would fit on my existing battery trays on their sides - good thing LiFePo batteries don't care about mounting direction.

[NoGas]

At the Q Big Tent this year, Battle Born’s 100 Ah batteries (1,200 Wh) were On-Sale for $850 each. It’d take 3 of those to equal the one KiloVault 3,600 Kh. That’s $2,550 vs $2,279. One KV is 84 lbs and 3 BBs would be 90 lbs. BBs come with their own internal BMS. Assume KVs do as well since both say the entire 100/300 Ah of each battery is available before the battery auto shuts down to protect itself.

However, connecting multiple Lithium batteries together is not as simple as with lead acids. On the KV spec sheet they are very specific about balancing. That’s because ALL of the individual CELLS in ALL Lithium batteries of a coach bank must be balanced to the same exact charge state. If connecting multiple 12V Lithium batteries to one charger, it’s critically important to balance the SOC for all batteries in a bank AND to keep them balanced. Just charged my scooter last night (4 x 12v batteries with 16 cells total). My scooter has ONE BMS taking care of all 16 cells. You can see on the display shown in pic below, that now every cell is perfectly balanced. How one would do that with each battery having it’s own BMS when using a single charger, I’m not sure.

Thankfully with my 6 L-16 AGM’s (1,260 Ah with 600 Ah usable at 50% DOD), I don’t have to worry about that

The only direction Lithiums & AGM’s cannot be mounted is upside down. BTW - the Geeks didn’t mention that Lithiums are highly sensitive to high temps as well as low. Basically, they like to be at the temperatures you like and will work perfectly in that narrow temperature range.
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[badandy]

If they are connected in parallel then there is nothing to worry about. Each series string will balance itself.

[NoGas]

Hey Andy - Over 6 years of use I’m not confident two or more batteries each with independently operating BMS’s that have no direct control over a single charger - is the way to go. Do you know if self-contained lithiums like the BB and KV products balance their individual cells internally?

I’ve found that one or two of the 16 individual cells in my scooter pack sometimes “go rogue”. At or near it’s fully discharged state (BMS low voltage protect is set to disconnect the pack at 25% SOC), those cell voltages will drop 1/2 volt lower and their cell temps rise about 10 degrees higher than adjacent cells. In my case and with my single BMS employing individual cell load balancing, it handles balancing for all cells in the pack as it charges the pack. The result 3-4 hours later is fully charged near perfectly balanced pack that looks like the picture above.

[badandy]

If the "rogue" cells are always different cells and you see it all over the pack I would blame your BMS. Most BMSes used on these kind of lifepo4 cells also do active cell balancing and also don't do a very good job of anything except smoking batteries. You are better off without it!

If the rogue cells are always the same two then you need to replace them because they have failed.

Half a volt and a 10 degree temp rise is a HUGE alarm! Canary in the coal mine style!

None of this is due to a series/parallel connection.