Dual-Purpose, Starting, and Deep Cycle Battery Testing and Recovery



There are a few types of car and boat batteries that every craft owner should know about, and information on how to recover them is particularly important. If you ever find yourself in the situation where your car or boat engine simply will not crank at all, knowing the difference between the battery types and the proper procedures for testing and recharging them is very helpful.

A dead battery is often to blame for non-cranking engine issues. And since a dead battery is pretty much guaranteed to happen to every car and boat owner at some point, the following information will prove useful in diagnosing and replacing it.

How Do Dual-Purpose Batteries Work?

Dual-purpose batteries are perfect for purposes that demand both starting and deep cycle operations. They provide strong crank amperage to simplify startup, and low amp draw operation for dependable auxiliary energy. This makes them a nicely balanced compromise between the distinct requirements for starting operation and deep cycle/low amp draw operation.

How Do Starting Batteries Work?

Starting batteries for boats and vehicles are very similar. These batteries can provide a lot of electricity for a brief time period, but ideally need to be re-energized as soon as possible after being operated, and they cannot handle deep discharges. These are suitable for single-battery use on small boats, runabouts, mini-watercrafts, and other vessels with light power loads in which the engine stays running.


How Does a Deep Cycle Battery Work?

Deep cycle batteries are built to provide a gradual, controlled, lesser-amp energy discharge – from several minutes up to several hours – for deep cycle operations, which includes using a trolling motor or heavy-duty boat accessory loads such as depth calculators, fish locators, radios, sensors, lighting, refrigerators, powering a house, and other functions.

With these batteries, the electrical energy emanates from deep inside the plates rather than from the surface like starting batteries. Consequently, deep cycle batteries are specifically designed with heavier, denser plates and fiberglass supports, specialized energy-generating active materials, and distinctive heavy-load separators.

Because of these functions, the battery is able to stand up to the possibly harmful effects associated with constant deep discharges and recharges. The thinner, unsupported plates in a starting battery is unable to cope with this kind of continual deep cycling, and will usually go dead pretty quickly.

How to Test Old Batteries

1. If you’re testing more than one, use a permanent marker to mark each battery being tested in its corner. This way you can easily keep track of which batteries have been tested and which have not, and will have no trouble putting them back in the correct order.

2. Detach the battery or batteries from any inverters and current regulators.

3. Test every battery with a digital multimeter and mark the value digits on the top of each one. For batteries that register lower than 5.25 volts, tag them as “dead” and dispose of them safely.

4. Test battery cells with a gravimeter and write down their numbers by the cap of each one. When the variation between the highest and lowest cell value is greater than .050 (or 50 points), these batteries should also be labeled as “dead” and disposed of.

5. Reattach the working batteries in reverse order using the numbers you labeled in each battery’s corner during the first step.

6. Check to be sure all battery contacts are firm and that all battery cells are properly hydrated.

7. Reattach the batteries to all inverters and current regulators.

Battery Recovery Plan

1.  After testing and reconnecting your batteries, crank up the power generator and let it go through a recharging cycle until all batteries are fully charged.

2. Let an equalization cycle run for about three hours.

3. Detach the batteries from any inverters and charge regulators and let them sit out overnight.

4. Retest every battery with the digital multimeter and mark their digits on the top surface of every battery.

5. Retest every battery cell with the hydrometer and mark their digits close to the cap of every cell.

6. Reattach the inverters, leaving the current regulators detached.

7. Perform a load test on the batteries and record the results.

8. Recharge the batteries and record the final load test results.

9. Compare the load test results to determine how successful the battery recovery plan was and the current energy efficiency of the batteries.

10. Recheck every battery with the digital multimeter and once more write the numbers on each battery top. If any battery registers lower than 6.1 volts following the load test, tag them as “dead” and get rid of them.