Battery question

I need to get new batteries for trolling motor i cant fit two d31 optimas but i could fit a d34 and a d31 would that be okay or should i get two d34s if anyone knows please tell tx

Not 100% sure on this, but I have been told in the past to keep the batteries the same size as your only as good as the smallest/weakest battery. Not sure if that is accurate info that I have been given or if it might depend on if you are running the batteries in Parallel or in a series for it to be true. I have always kept them the same size and when I need to replace one, both are replaced.

To my knowledge you want them to match…

I have always been told you need the same battery and they should be the same “age” meaning you should replace them all if that is what needs to be done. I do not know the reasons for this but I am sure someone with some battery expertise will help explain the theory.

I just did some battery research due to thinking both of mine were bad. I cant remeber the web site but that was my findings also. My batterys wouldnt charge on my onboard charger due to too low voltage. I put them on a old car charger and then put them back on the onboard. Been out 2 times on them now. Seem to be working good. Whats the deal with the onboard charges and drycell batterys? I have a minnkota charger and it says for wetcell only.

As Otis Eyes points out, you should have matched batteries.

If one has a larger battery and a smaller battery wired in parallel and of equal voltage, then naturally, as one uses current from the system, initially equal amounts of current would be drawn off each battery. Since one is smaller than the other, there is going to be a point at which the smaller one begins providing less current and it’s voltage would then drop below the voltage of the larger battery. At this point, the larger battery will be the primary supply of current (it has higher voltage) but also begins discharging through the smaller cell to charge it (which is not 100% efficient process).

For this reason, it is best to have the same size batteries as they will discharge more uniformly and provide the best extended life.

As mentioned by Otis Eyes, when wiring batteries in parallel, it would be best to purchase both cells at the same size and same time since they will then be matched in capacity at the initial time of purchase and being exposed to similar loading, will degrade similarly over their service life.

If the batteries are of different sizes and service, then it would be best to only attach one at a time to the trolling motor and/or other load devices to maximize your reserve supply.

tx i will get two d34 they should be good

Link to battery information

Above is a link to an explanation of battery construction and why the voltage & current drop with usage and age.

Huntfishhastings,

Newer charges have over current protection to avoid burning out the charger’s electronics. If the output is shorted or too low of voltage, then the charger will shut itself off. Older chargers did not have this protection which is why you could hook the batteries up and get then to take some charge. Once the initial charge was restored, then you could have placed them on your newer charger and it would have charged them up.

Regarding wet vs dry cells… The lead acid wet cells have a charged voltage of about 12.6V (2.1V per cell) where as dry cells have a charged voltage of 1.2 V per cell.

The wet cell (lead acid) chargers are designed to charge at a higher voltage. Both due to the wet cell having a higher voltage, but also at a higher current as this kind of cell generally has more capacity than a dry cell and is tolerant of a higher charge rate. Typically the wet cell charger will provide a higher current of around 0-6A and be able to safely charge the lead acid battery.

The amount of current that is used is proportional to the battery’s size. For small 4-6 pound batteries like motorcycle or sport vehicle batteries, one can examine the manufacturer’s recommendations, but one will find that it calls for 0.5 – 2A max for 30 mins to 2 hours depending on the charge rate. Smaller vehicle batteries would be charged using a peak rate of around 4A and large batteries, up to 6A max.

Having too high of current or overcharging a battery results in heat being generated. The weakest cell in a battery will charge fully first and then will begin to heat up and become hot due to internal resistance. The heat will boil off the water in the battery and can cause the plates to deform and short leaving a dead cell and can even cause an explosion from the hydrogen gas created internal to the call by the current passing through the cells water (electrolysis).

Dry cells have a lower voltage, so when placed on a wet cell charger, will be charged with a higher current, which will lead to heat and generation of gases internal to the battery. The dry cell then will burst and leak acid.

In general the dry cells are required to be charged at a lower current for an extended period of time. Recent dry cell smart fast chargers are designed to detect temperature and the internal resistance of the cells to determine when to quit charging to avoid overheating.

An exception was the 15 minute rechargeable cells produced by Ray-O-Vac a few years ago that had a device internal to the battery that stopped the charging process based on the cell temperature. This allowed higher current to be used for a short charge time while protecting the cells against destruction by heating.

I used these 15 minute rechargeable AA cells for about 6 years in my digital camera for kids sports, etc without having a single failure. They had very good life under higher loads and recharged in a very short time. However, Ray-O-Vac recently quit making them and has a different line of rechargeable cells now. I found that they are still sold on the internet, so will be getting some additional AA cells to cover for the next 20 years requirements!