Fish Finder Battery Revisited....

[JGibson]

I've searched here and found a few posts on using the small sealed batteries for fish finders. My question is, using a 12v 7ah battery, how long will it run one without having to charge it? I do alot of catfishing and I am usually on the water for up to 5 hours, I'll be using it the whole time. Would one last that long off of one charge? What about a Lawnmower battery?

 

[gnappi]

I've searched here and found a few posts on using the small sealed batteries for fish finders. My question is, using a 12v 7ah battery, how long will it run one without having to charge it? I do alot of catfishing and I am usually on the water for up to 5 hours, I'll be using it the whole time. Would one last that long off of one charge? What about a Lawnmower battery?

I use a single 35Ah Solar brand AGM deep cycle battery for all of my electronics (DF, bilge, lights, horn, fan, GPS, Gopro (2x) and USB charger for my phones) and don't worry about power at all. The one at Harbor freight is something like 25 lbs, and $60 and no core charge. They're too light and inexpensive (IMO) to worry about power needed and mine has lasted me over 8 hours on the water, and still had power left to take over when my two TM batteries got to where I'd prefer to recharge them rather than drain them too low.

Wal mart has similar batteries but I have only used their large deep cycle batteries for my solar lighting system.

https://www.harborfreight.com/12-volt-35-amp-hour-sealed-lead-acid-battery-64102.html

 

[Scott F]

How long it lasts depends on the depth finder. Years ago, I used the same battery on my Canadian fly-in trips and it would last the entire week powering a 4” b&w unit. We were cautious about our usage and shut it off when we didn’t need it. We never ran out of juice. Newer depth finders with larger, color screens, gps, side imaging will suck up power more quickly. If you know the amp draw of your unit, you can easily calculate how many hours of use the battery will last.

 

[MrGiggles]

Most units draw somewhere in the neighborhood of 500ma, some more, some less. The current draw of any particular unit is usually always listed in the specs. At 500ma, you should get about 14 hours from a 7ah battery.

Amp hour rating is a measure of current over time, 7ah would be 7 amps for 1 hour, 1 amp for 7 hours, or however you wanna slice it.

 

[maintenanceguy]

A lead acid batteries voltage drops as it is used. Once they hit about 1/3 charge the voltage is getting too low to be useful. They will deliver the full 7Ah charge but not at the full 12V you need. Every battery is different but let's assume you'll get 2/3 of the rating or about 5Ah.

Amp hours (Ah) is just what it sounds like: Amps multiplied by hours. If you have 5Ah available, you can get 5 amps for 1 hour (5 x1= 5), or 1 amp for 5 hours (1 x 5 = 5), or 2.5 amps for 2 hours (2.5 x 2 = 5), etc.

You need to know the amp rating of your fish finder - this will be somewhere on the fish finder. If MrGiggles is right and it draws 500ma, that's half an amp. 5ah / 0.5A = 10 hours. Formula is: BatteryPower(Ah) / AmpsDrawn(A) = Hours(h)

 

[JGibson]

So I bought a sealed 12v 7ah battery just to try it out. It says Max charging volts is 2.1amps. Will it hurt the battery to charge it with a 3amp charger?

 

[maintenanceguy]

So I bought a sealed 12v 7ah battery just to try it out. It says Max charging volts is 2.1amps. Will it hurt the battery to charge it with a 3amp charger?

I would go for it but...a 3A charger will deliver up to 3A, depending on the voltage of the drained battery. It won't deliver 3A all the time, and might not ever deliver 3A but it could. As the voltage of the battery rises, the amperage delivered will drop. The amperage delivered depends on the difference between the charger's voltage and the batteries voltage. Your charger might deliver the full 3A for a few minutes but the battery voltage will quickly rise, lowering the amperage delivered.

I think damage is unlikely. Considering the low cost of a 7ah battery, I'd take my chances and just do it.