# Why does the voltage of a lead-acid battery drop with load?

My solar power system contains a lead-acid battery but as soon as I use the inverter to power some load, the voltage drops instantly by 1 volt.

Why does this happen? And is it proportional to the load (bigger load = bigger voltage drop)?

• Did you try to search for this information on your own? For example reading electronics.stackexchange.com/questions/9183/… – pipe Jul 28 at 11:11
• Thank you but I already checked both before posting : no and no. Check "Andy aka" post for an amazing answer. – bob dylan Jul 28 at 11:33
• Just to weigh in on that, it's not the first time I've seen that in stack "Electrical". Often people are voting to close / put on hold without reading or even knowing anything about the subject of the question. (Just copy pasting the question in their search bar ?) Maybe it's a recurrent problem that should be addressed. – bob dylan Jul 28 at 11:55
• I’ve nominated for a re open – Andy aka Jul 28 at 14:59
• So my question is a duplicate of a closed question about Lipo batteries with no accepted answer. Nice ! – bob dylan Jul 29 at 11:57

• It is, according to the answer of electronics.stackexchange.com/questions/57508/… . If you can't do a full capacity test, simply measure the instantaneous voltage drop with a known large load, and again graph the results. – bob dylan Jul 29 at 14:08