care and feeding of big (8ah) rechargeable batteries?

This summer I got a sonar unit, an eagle cuda 240 and a pair of he-uge cabelas 12v 8ah batteries.

why an extra $25 battery? so I'd always have one charged for that big trip.

After my last 5 or 6 trips, my first battery is still at 12.2 volts, it seems to go down about 0.05 volt each trip.   
I just left it in its lock'n'lock box, and didnt even take it out of the boat between trips as it was sealed against
the elements in the box.

So I have not yet dealt with re-charging, swapping, storing, etc.

but I feel like I should be doing something with my batteries, I'm just not sure what.

How low should I let it go before recharging?

What is the best way to deal with batteries in the off season?

Thanks for any advice from the veterans out there,

J

I have a Power Sonic (Computer Battery) 12 volts and 7.0 amps. It is around $16.  But, the Power Sonic Automatic Battery Charger 12 volt 0.50 A is the thing that is pricey.  Around $35 to $50.  I charge mine about every 3 trips out.  Sorry, don't know about long term storage.  I have no downtime.  Got to fish at least one day a week.....or I don't feel "Good".

Ken kickfish

maybe I am over-thinking this one.

how low is it when you charge it again?

J

Don't really know but usually on the 4th day it will stop working around noon time.  The charger has a quick charge and a long cycle mode. Auto shut-off too. I usually take it off after about 6 to 8 hrs.  I once did see Mike (Sturgy) battery and it was splitting at the seams.

Ken kickfish

It really depends on what type of re-chargable battery you are using.

http://en.wikipedia.org/wiki/Rechargeable_battery

If you are using some sort of lead-acid battery, usually it is best for the battery to maintain a constant low current trickle charge when not being used, although it is also fine to just fully charge the battery and then let it sit, since lead acid battery's loose only a small amount of charge over time (~5%/month). 
I use a lead-acid battery from an un-interpretable power supply (UPS) so when I am not in the water I just put the batter in the power supply which then provides a trickle charge and the batter is ready to go for the next trip.

Brian 3d

I have a 7ah lead acid rechargable and I try to store it charged, but more often than not I use it for a trip and leave it untill the next trip when I charge overnight before I go.  It has lasted me 3 years so far with no problems.

MolBasser

With the light current draw that we have from our finders, I think the lead acid batteries should last a long time regardless of how you treat them, as long as you realize that they NOT like NiCad and other forms of recharagbles that have do have memory.  With NiCad and some other bats, it is best to run them all the way down before recharging them, but with lead acid batteries this would be a bad thing to do.  Unless you have a deep cycle lead acid battery (like for a trolling motor) it is best to keep the battery as near fully charged as possible. 

With my lead acid battery and fish finder combo, I calculated that I should be able to run it for nearly 80 hours, so one 8 hour session only uses ~10% of the charge, so even if I did not charge it right away, the bat should be fine.

The lead acid bats are a bit heavy, but if you can get 3+ years like Mol, that is not bad for the price.

Brian 3d