starting with battery maintainer connected

My 308 tends to run out of juice after three weeks and I have yet to track down the cause. But I do have a battery maintainer installed, so it's easy enough to plug it in a couple hours before a drive and no problems. Last week I tried to hop in and go, but there wasn't enough power to turn the engine over, so I plugged it in. After just 10 minutes I hoped it had enough because my wife and I wanted to head out, so I got in and started the car without unplugging it - totally forgot to unplug first. It turned over immediately like the battery was fully charged, effectively a jump-start. After that we drove the car all weekend with no ill effects, and the alternator charged the battery right up.

I don't plan on making a habit of this, but what are the potential issues with using a battery maintainer as a jump start? I don't think I did any damage and the car ran perfectly afterwards.

 

sounds safe to me, i dont think the trickle charger isnt sending anymore power than allowed, just enough to charge i believe.

Good read here.
http://en.wikipedia.org/wiki/Trickle_charging

Float charger

A float charger differs from a trickle charger in having circuitry to prevent overcharging. It senses when the battery voltage is at the appropriate float level and temporarily ceases charging; it maintains the charge current at zero or a very minimal level until it senses that the battery output voltage has fallen, and then resumes charging. It is important to note that the appropriate float voltage varies significantly with the construction of the battery and the ambient temperature. With the appropriate voltage for the battery type and with proper temperature compensation, a float charger may be kept connected indefinitely without damaging the battery. With a 6-cell (nominal 12V) lead-acid battery the correct float voltage drops by about 0.15 V for a 5°C rise in ambient temperature. Not compensating for this will shorten battery life either by over- or under-charging.
[edit]Trickle charger

A trickle charger, on the other hand, will charge no matter whether the battery is fully charged or not, so it needs to be connected and disconnected periodically. Trickle chargers will work to keep the battery charged, if used once a month or so for a day or two, but the float chargers can be left connected indefinitely without potential harm to the battery

 

True, but the battery must be fully charged for the maintainer to work properly. I leave my maintainers on for months and have done so for years. Never a problem!

You can get them from Harbor Freight for under 10 bucks. I even put one on my lawn tractor during the winter months. Just started it yesterday and battery was still fully charged.

 

Thanks. Mine is a float charger by that definition, so no danger of overcharging. I was just wondering if there was a risk to the electrical system by inadvertently starting the car with it still connected. I wouldn't think so, and the car has been just fine, but it never hurts to ask.

 

I use battery maintainers ("float chargers") on all my cars and bikes, and love 'em. IMHO, a maintainer (or trickle charger) does not put out enough amperage to fry the electronics or cause any damage if you start the vehicle with it attached.

 

The worst that might happen is you could pop a fuse. A battery maintainer only puts out about 0.5 Ma.