Cost aside, a 400ah Sealed led Acid/Gel battery bank at 50% Depth of Discharge would give me 200ah, ideally or lets be kind and say 150ah on a 24v system. Why then would suppliers recommend getting a 24v 100ah lithium battery, on the same system and on the same loads? This is a Pv/Grid coupled system by the way, with 12 x 250w panels with an MPPSolar Chinese Inverter.

Please help.

When a Lithium battery is at 100% SOC it is fully charged, and it can charge rapidly. Acid/Gel may appear full, but still need +- 24 hrs trickle to be fully charged.

Lithium also has an intelligent BMS protecting it, whereas, Acid/Gel don't come with built-in BMS, your inverter needs the correct settings or the batteries will be destroyed.

57 minutes ago, TimCam said:

When a Lithium battery is at 100% SOC it is fully charged, and it can charge rapidly. Acid/Gel may appear full, but still need +- 24 hrs trickle to be fully charged.

Lithium also has an intelligent BMS protecting it, whereas, Acid/Gel don't come with built-in BMS, your inverter needs the correct settings or the batteries will be destroyed.

Many thanks for your swift response. I'm fully aware of that caveat on Acid/Gel batteries. It's just on face value, it makes sense to go the Gel/Acid route when simply looking at the capacity of 200ah on Gel/Acid vs Lithium at 90ah for 90% DoD, so why would an installer recommend lithium. My system is grid-tied with PV, so ideally at most times, I should be able to trickle charge the Gel/Acid at least 2-3 times a week to full capacity. However, because my load is significant, if I have a blackout, then lithium doesn't give me enough and I have to further reduce my non-essential loads.

On 2022/01/01 at 7:15 PM, Moffat said:

then lithium doesn't give me enough

OK, from my experience, lead acid do not last with a 50% DOD, so if you plan on 50% of the 400Ah bank, then expect in under 5 years to fork over some more dosh for a new bank... also, let us make some basic assumptions here, a 400Ah bank of lead acid, should probably not be running at more than 80A current peak, which will give you 2.5hours for your 50% DOD... or is the current lower but expected to deliver over a longer period... the obvious answer, I would think is to size the Lithium side with enough energy and even on those, try and keep 20% in the battery/ies before re-charging... so budget for a 80% DOD max on the lithium end, you should, if you treat them nicely get near enough to 10 years out of them, I'd imagine.

22 hours ago, Kalahari Meerkat said:

OK, from my experience, lead acid do not last with a 50% DOD, so if you plan on 50% of the 400Ah bank, then expect in under 5 years to fork over some more dosh for a new bank... also, let us make some basic assumptions here, a 400Ah bank of lead acid, should probably not be running at more than 80A current peak, which will give you 2.5hours for your 50% DOD... or is the current lower but expected to deliver over a longer period... the obvious answer, I would think is to size the Lithium side with enough energy and even on those, try and keep 20% in the battery/ies before re-charging... so budget for a 80% DOD max on the lithium end, you should, if you treat them nicely get near enough to 10 years out of them, I'd imagine.

Sadly... solar and more to the point batteries and their usage, always seems like going down a rabbit hole. Due to cost constraints, I have opted to go the Gel route and with a DOD of 40%. Eventually when I can afford it will then replace the Inverter with a 48v variant and go the lithium route. My current MPPT has a maximum draw of 60A, peak. I've only stressed it a couple of times when I had load shedding going for over 2days and needed to use and iron, otherwise my current battery bank of 100ah x 6 batteries for a 24v system has served me since 2014 till last year when they reached End of life and now no longer hold a charge.

Edited January 6, 20223 yr by Moffat