Question about lead acid batteries in series and bms.

[Shanimus]

I'm planning a 48v system and was either going to buy lifep04 cells and make a battery for it, but swap and shop has 16v 300ah datasafe agm batteries for cheap. If I get 3 or 6 of them and put them in series, I'm wanting to make sure they'll be safe and not get overcharged etc. and was looking for suggestions.

 

[Madco]

Any lead acid battery solution will not need a BMS. Pretty much any charge controller or AOI will accommodate lead acid batteries.

Three in series will work but 6 in series will net a terminal voltage of 96V. Maybe you meant two parallel strings of three batteries?

If you go with the AGM solution, watch out for excessively deep discharge cycles which will reduce battery cycle life. Most folks recommend discharge no deeper than 50%. That recommendation applies to all lead acid batteries. With lithium, the recommendation goes to 80% maximum discharge. As a result, there is a fair amount of capacity remaining with lead acid batteries that is "untouchable". You can use it if absolutely necessary, but doing so will shorten your battery life.

 

[Solarcabin Channel]

How are you charging them and using them?

 

[Madco]

My present systems don't use AGM batteries. I use 370 AH L16 motive batteries or LiFPO4.

All lead acid batteries are charged the same except AGM batteries are not equalized. You just set the appropriate parameters in the charge controller or AOI and you're done.

I've used AGM in several designs and they perdorm well-just treat them gently on the discharge and you'll be fine.

BTW, I'm not suggesting you use one battery technology over another, but lithium may be a better choice. It is highly application specific.

 

[MichaelK]

swap and shop has 16v 300ah datasafe agm batteries for cheap. If I get 3 or 6 of them and put them in series, I'm wanting to make sure they'll be safe and not get overcharged etc. and was looking for suggestions.

These may not actually be a good choice for an off-grid system. The word "datasafe" suggests to me that these are standby power batteries that are NOT designed for daily cycling.

There's the common practice of selling used batteries that appear to have utility just to get rid of them. In actuality what you are really doing is paying them to become their battery disposal service. If they sell these batteries to you, they won't have to pay the recycling charges to get rid of their marginal scrap.

 

[Shanimus]

Ended up getting Lifepo4 batteries.