DIY solar battery storage Humsienk golf cart battery not discharging

Had something eerily similar happen with my motorhome setup last summer. The battery would charge fine, sit at a healthy voltage, but the moment I put any meaningful load on it — nothing. Flat refusal.

Turned out my BMS was tripping on over-current protection almost instantly, even at relatively modest loads. The default settings were absurdly conservative straight from the factory.

A few things worth checking in your situation:

• BMS settings — can you connect to it via an app or Bluetooth? Some budget BMS units ship with discharge current limits set far too low
• Cell balance — if one cell is drifting low, the BMS will cut discharge to protect it even when overall voltage looks fine
• Connection resistance — a loose or corroded terminal can cause a voltage drop that triggers protection circuits under load

I've not used Humsienk specifically, but golf cart batteries converted for solar storage can be a bit temperamental if the BMS wasn't designed with static solar use in mind — they're often spec'd for the burst loads of a motor rather than sustained household-style draw.

What does your BMS read when you apply the load? And what are you using to monitor it — anything like a Victron BMV or similar shunt meter? The data from that moment of cutoff would tell you a lot.

Would love to hear what others have experienced with repurposed golf cart cells — there's quite a few of us on here running unconventional setups and the collective knowledge is usually worth tapping into.

@Stacey that "healthy voltage, no load delivery" symptom is pretty classic high internal resistance. The cells look fine sitting there but they can't actually sustain current under demand.

Worth doing a proper load test rather than just checking resting voltage — a multimeter won't tell you the whole story. Check what the voltage actually does the moment you throw a meaningful load on it. If it drops like a stone then recovers when load's removed, that's your culprit.

With golf cart batteries specifically, sulphation is often the root cause, especially if they've ever sat discharged for any length of time. Some people have luck with a slow desulphation charge cycle but honestly, if the battery's older, sometimes it's just done.

What BMS or protection circuit are you running with it?

@Stacey had this exact scenario with my shepherd's hut setup — turned out the individual cells had wildly different state of charge despite the pack looking healthy at rest voltage. Worth doing a proper cell-level check rather than just measuring at the terminals.

@WingAndPrayer is right about internal resistance but also worth checking if there's a BMS cutting out under load — mine was doing a protection shutdown almost instantly because one cell group was sagging below threshold. Looked like the battery was refusing to discharge but it was actually the BMS doing its job.

Do you have any way to monitor cell voltages individually? Even a basic cell meter helps enormously. Golf cart batteries being flooded lead-acid I'd also check for sulphation — that'll give you exactly this symptom.

@Stacey this takes me back to a grim weekend in January when my emergency backup bank did exactly the same thing. Sat there looking smug at 12.8V, then the moment I switched the inverter on — voltage cratered to 10.2V within seconds.

What nobody mentioned yet: check your connections first before condemning the cells. I spent two days suspecting the battery itself before discovering a corroded terminal bolt that was creating just enough resistance to fool the resting voltage reading entirely. Cleaned it back to bare metal, applied some copper grease, and suddenly the whole thing came back to life.

Golf cart batteries especially — those chunky terminals are deceptive. They look solid but corrosion works its way underneath where you can't see it. A proper load test will confirm either way before you start pulling cells apart.