Add another battery to the bank

jcon4

New Member
Joined
Nov 15, 2019
Messages
3
Just curious to know if I add another battery to an existing bank... is there any problem?
Specifically... in my RV I have a 1year old 12v Renogy 170ah lithium ...that's been great... If I bought a new one say the same battery and add it ... would that kinda throw things off!?
I seem to think they need to be the same age... because of reasons I'm not sure of..
Anyone?
 

FilterGuy

What, me worry?
Joined
Nov 26, 2019
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4,458
Location
Los Gatos CA
I am assuming you would add the new one in parallel.

It should work fine assuming the existing battery is not too degradated. What will happen is that when the two banks get low, the weaker battery will stop contributing.....When the bank is charging, at the top end the weaker battery will be in 'constant voltage' mode a little longer.
 

tictag

Off-Grid Enthusiast
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Dec 31, 2019
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Location
UK
It should work fine assuming the existing battery is not too degradated.
The thing is with LFP batteries is that they don't degrade (aka 'age') anywhere near that of say a lead-acid. Even if you cycled your Renogy every day, that's still only 365 cycles for a battery that's probably rated for 5,000 cycles - and even that is just down to 80% capacity!

If you wanted to be super, super careful you could do a capacity test on your Renogy and let's say it comes back at 95% of its original capacity, most people don't discharge their LFP batteries beyond 90% DoD so the BMS would never actually have reason to shut off the battery.

In short, you'll be fine :)
 
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