[topcat]

I noticed after I had my cheap battery charger charging the car battery that the starter motor turned over faster. I guessed that the battery charger had put more "juice" into the battery than it would normally get from the alternator.

If I can slightly over-charge the battery before each trip, then the alternator would not need to put so much in during driving, thus easing the load on the engine and ultimately using less fuel.

This led me to thinking whether I could hook up a semi-permanent system to allow this to happen overnight. I already have a block-heater IEC mains lead going in, so maybe I could use this to power a small lightweight charger kept in the engine bay, permanently connected to the battery. Then when my block heater is powered, my battery is getting topped up too.

So I bought a CTEK charger designed for permanent connection. But this only charges to 14.4V, (the same as the alternator). I do not see the same effect on the starter motor turning faster after I have used this CTEK charger. CTEK do another model which charges to 15.0V, but I've blown the budget now...

So I found an old PSU from a Toshiba laptop, which gives out 15.0V (up to 4Amps), weighs less than 1Kg, and has very low ripple (measured < 10 mV), and very low back current drain (<10 mA). I've done some tests on an old battery (off the car). Now I'm considering using this permanently connected under the hood. i.e. clamp it near the battery.

Questions:-
- Is it safe? I'm pretty happy that the chargers are about as safe as you can get, millions of Toshiba laptops around. Never heard the chargers catch fire.
- Will 15.0V charging kill the lead acid battery eventually?
- Will the alternator adjust its load to take account of the fact the battery is already charged? (Car is 2005 Toyota Celica 1ZZ-FE engine, surprisingly quite efficient!)