Battery question

All,

I have contemplated the move to a AA battery pack and I have some questions regarding batteries.  I hope that some of you have the specific knowledge to help me.

Currently, I have a 7aH gel cell battery that works very well, but is heavy.  My unit draws 350mA and thus I should get about 21 or so hours of use out of that battery and that is about what I see in the field.  Fine, pretty easy, one battery and I know how much my unit draws and how much the battery has.

Here is my question.  Let's take the example of a 2400mAH rechargable set.  You hook the batteries in series to get to 12v.  Is the whole series still 2400mAH?  Is it more?  less?

I have an 8AA harness and took it out to the kelp the other day.  The voltage into my unit (measured by my unit) dropped from 12.1v to 9.8v in about 4 hours using radioshack AA batteries.  Does this seem right?  In a similar time frame, my gel cell will drop maybe a tenth of a volt.  Can I expect to have to charge (I will get the 2800 mAH recharge and a 10AA harness) my batteries every trip?  Will they last 8hours.  That is the calculation (if a series of 2800mAH is 2800mAH) with a 350mA draw.

Seems sort of short, but I just love how small and light the AA harness is, but 8 hours kind of sucks....  And not only that, but in terms of voltage, what are these batteries going to deliver after 4 hours.....

I guess I need to search the web for performance data.

Any insight would be appreciated.

MolBasser

The data in THIS .pdf would seem to indicate that mAH is a fairly variable thing depending on the power draw.

The chart included would indicate that with a 25mA draw the energizer AA battery has a 2800mAH life but if you increase the draw to 500mA the life plummets to about 1500mAH.

This sucks!  That would mean (if a series of batteries has the same amp/hour as a single) with my 350mA draw with energizer AA batteries (these are the normal not rechargable I need to look for that data), that I only have about 1800mAH and thus about 5 hours of usage.  That totally sucks, and would mean that I need to keep using my gel cell.......

MolBasser

Hmm....

The DATA looks FAR better with rechargable batteries.

They seem to hold voltage much longer.  This is actually more usable, but still sort of short.

I would definately need to charge batteries for every trip, and makes multi day trips with these batteries out of the question.

Guess I will leave the ability to switch between light and convenient and heavy and long lasting.

MolBasser

Kind of funny watching myself answer my own questions.....

The internet is a wierd thing....

Hope all this talking to myself helps some other people!   

MolBasser

Chris,

Everyone is different, but while I considered the AA NiMh route, I eventually just went with the 4.5 A 12 sealed lead acid battery. Sure it's a little bit heavier than a bank of AAs, but it charges right out of the cigarette lighter, and has longer battery life. Totally KISS.

Scott

I use a 12v 1.3 amp lead acid battery that  is less than one lb in weight. Its relatively light and compact and would almost be the same weight as 8 AA batteries in a holder. It can be had for as cheap as $8 on the internet and it works  fine for me. It lasts all day though and since I've only done day trips, I'm not sure how may days it would actually last.

your soliloquy made me look up the draw in the manual for my sonar unit and calculate the estimated battery life.

might be interesting as a comparison.

I went with the eagle cuda 242 ($80 from cabelas) and an 8ah battery just because that's what was in the cabelas online store and I didn't want to think too hard.

I did rationalize that a single beam lower power unit would mean I'd have longer battery life but I wasn't really sure how much.

the manual says it draws 170 ma without the backlight, 240 ma with the backlight.

Since I mainly operate without the backlight I should get something approaching 8*1000/170 or 47 hours of sonar before  I have to mess with the battery.  For me this is kind of cool, because I have a setup where I basically leave a lot of gear on and in the boat when I transport and store it to try to reduce prep time for fishing. when you spend 5 hours  selecting your lures, you need all the buffer you can get, 

J