by GeorgeTelford » Tue Sep 20, 2005 3:30 am
Hi
You should not regularly take your batteries below 50% if you want them to last. So then you have a 105 ah
But depending how you charge your battery it may not start at 100% Charged, if you charge via an alternator the battery will only charge somewhere between 65 and 70%, so in effect you may have only started with 136 ah, take away the 50% (105 ah) you should not be using and now you only have 21 ah to play with.
If you use a standard onboard leisure charger (convertor in US?) then the situation is very similar, we have a similar type in UK doing discharge tests, I found that if you leave the on board charger running for 4 weeks constant with no draining loads it gets to about 90% charged. Use the onboard charger overnight after a trip and you get about 70% (from 50% discharged start)
The above is why I have a Smart regulator to make the alternator operate as a 4 stage charger, this ensures the leisure batteries get fully charged very rapidly when driving, and a 30 Amp marine charger/power supply for when hooked up.
Incidently if you fully charge a leisure battery and then drive with the battery connected to the vehicle alternator, you will lose charge until battery gets down to 65-70%
Here are the notes I made of an experiment a year or so back
from fully charged at 12.93v (measured 12 hours after coming off the Sterling charger) connected bulb, it took 6 hours and 17 mins to reach 12.2v (ie flicking over backwards and forwards from 12.3v)
It was then fully recharged on the Sterling, allowed 13 hours to settle the voltage, reading was 12.94v flash 12.93v, the engine on the iveco was started, then I connected the battery using a good solid cable as before and drove this morning for 1 hour 14 mins, as soon as I got back it was connected to the same bulb (55w halogen) connected at 12 : 12 today, it started flashing between 12.3 and 12.2 at 5 : 37 PM today
Same battery, same full charge by Sterling, only difference 1 hour 14 mins of extra "charging" as knocked off 52 mins off usable power !!