Originally Posted By: wrcsixeight
I have a similar old school manual charger but 10 and 2 amps outputs. When I put my ammeter on it it was only doing 6 amps in to a well depleted battery, which was disappointing. as it shoudl have been doing 10, or perhaps more.
901M is right, that charger can indeed overcharge if left on for too long.
Harbor freight sells the cen tech digital multimeters, and sometimes gives them away free with coupon and another purchase. Sometimes they are just 3$.
Not a professional tool but it is accurate enough for checking battery voltage.
http://www.harborfreight.com/7-function-multimeter-98025.html
These can be calibrated too by opening it up and moving a small potentiometer within with a screwdriver while looking at a known accurate DMM.
Your existing charger can safely be used, but not overnight. In general The less amperage the battery is accepting the more charged it is, but as far as it actually being 75% charged when you hooked it up, that is not accurate.
I thought it was one of the more modern 'smart' chargers which renders a guess as to state of charge at the initial voltage when first hooked up.
I can't guess at the state of health of your battery, only that 2 hours at 6 amps output did very little to actrually recharge it to full if it was only 25% charged.
With that charger, remove the battery caps, wear eye protection and shine a light into the cells. Put charger at 6 amps on it until you see about 1 bubble rise to the surface every second, then switch it to 2 amps. If bubbling continues , or when it restarts, then let it go for another half hour then terminate charge.
It would be safer to remove the negative cable from our nissan, but you will lose your stereo settings.
You can likely get more useful life from your current battery if you recharge it, and any future battery would also last much longer if kept fully charged by a grid powered AC charger.
The cheapo Centech meter works fine for checking a battery that is not being charged. They are very sensitive to noise and won't give a reliable reading when the battery is being charged.
