I was requested to post it as a new question here: Lead Acid Battery charging from laptop psu so here goes the copy paste with an added video link I just uploaded:
I am new to lead acid charging and have been using a 19 V 5 A vaio laptop charger to directly charge the batteries, 2x used 12 V 75 Ah in parallel (=12 V 150 Ah) for a few months which in turn power some low watt LED lights and a 12 V table fan when main grid load-shedding occurs in this part of the world. I've noticed that the batteries can initially draw around 8amps from the 19 V 5 A PSU without overheating the PSU. The batteries no longer boil as they used to when charged four in series with the huge 48 V controller which was required to overnight recharge an electric autorickshaw (their first hand use) and now remain cool whilst charging, I haven't needed to top up the water in over six months either despite the driver having had to top them up 2-3 times a week previously.
I am wondering if it's OK or whether I need to reduce the voltage output from the PSU to ensure longevity of the batteries since the charger is usually left on until I switch the connector between the two sets of batteries which I charge and use alternately as the lights from one set begin to dim after 2-3 days. Any suggestions and links to diagrams if voltage reduction is helpful would be appreciated.
BTW, I also charge another set of four in parallel with another 19 V Toshiba laptop charger (trickle charges a few points of a volt every day), I've noticed that smaller laptop chargers (I've got a small pile of them sitting around) tend to immediately begin to heat up upon plugging in (possibly due to lack of intelligence or inability to regulate amp draw?) So there appears to be some sort of intelligent co-ordination between the branded high amp chargers and the batteries - just added that in case it helps in drawing a clearer picture of how things are.
Here's a video with the pulsating voltage multimeter readings:
I found this circuit for reducing the voltage, is it efficient enough to charge my larger batteries through? Or maybe if I added a few more LM317's in parallel in order to increase the load bearing capacity (datasheet shows max 1.5 A each) - and would the transistor cope despite this? Any other workarounds?