Cheap battery charger?

[TomtheElder]

I don't have much experience but just bought a used canoe and trolling motor to use for fishing. I bought a Walmart deep-cycle battery (I know - but price is a really big factor for me). Now I need a charger to go with it. Can I get by with their $30 auto battery charger or is there an important enough difference that I should buy their $50 charger that says it is for deep cycle batteries?

Also, I have read that it is important not to drain the battery more than about 50%, or its life is significantly shortened, and that means not draining it below about 10.5 volts. Is it really necessary to take a voltmeter out with me or is there an easy way to ballpark when to turn it off? Thanks.
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[gdn443]

I bought a charger at walmart for about $40.00, a Black & Decker. Has the deep cycle setting. I've drained mine down to 10% and it hasn't been a problem to recharge. I've had two rechargers that Cabelas sold me and they don't seem to last more than two years.
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[TomtheElder]

I didn't see a B&D but I will check it out. Thanks.

Any idea how far I can drain the battery without shortening its life, and how to tell when to stop draining it. Or is when the motor stops turning the best clue?
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[gdn443]

You'll know when the motor starts to slow down. It depends on how much you push it. My 55 lb thrust will run most of the day bass fishing and draw down to 25%
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[TomtheElder]

All day and only 25%? That is fantastic - had no idea that kind of duration was possible. I expect you have a better battery than mine, but then my motor is only 27 lbs thrust and only pushing a canoe, so I have reason to hope! I will let you know how it works out.
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