Let’s Get Ready to Check and Charge
Springtime means thinking about getting recreational vehicles out of storage. From motorcycles to boats or from lawn mowers to ATVs — they all require battery power. Even if the battery is stored correctly, we need to check it, test it and quite often, charge it.
A seasonal battery’s service life can be extended by as much as 50% by effective charging methods, procedures and a correctly matched charger. Make sure you:
- Visually inspect the battery
- Check fluid levels if applicable and fill only if needed
- Check the battery’s state of charge level
- Have the battery checked to determine whether it’s Good, Bad or somewhere in-between.
The following applies to multiple battery types and sizes, including motorcycle, marine, auto, etc.
Should I allow a deep-cycle battery to become completely discharged before recharging?
No. Lead-acid batteries do not need to be deeply discharged to be recharged. The opposite is actually better. Through various testing, we have found that there is a tremendous increase in service life through the number of cycles the battery will perform when it is not cycled to 100% depth of discharge. As an example, we have tested deep-cycle batteries and found that the battery will more than double its cycle life between a 100% DOD (completely discharged) and conducting 60% DOD levels.
Is it better to slow or fast charge a battery? What is considered too fast vs. too slow?
Generally, a slow charge is best overall. But what differentiates a slow vs. high recharge current levels? There are several things to consider. A charger can either add or subtract service life to your battery. Too fast of a charge overheats the battery. Slow charging (1-2 amp level) may not allow for an effective charge when time on charge and/or voltage regulation of the charger are not adequate.
Let’s choose a 100 Ah marine group 27 battery. A good rule of thumb is a charger size of 20 amps (1/5 of the battery’s capacity) is typically an effective initial current. You can choose a lower charge level, but it increases the time on charge.
Determine the battery type. This is important because of the differences among deep-cycle flooded, automotive flooded starting, motorcycle and AGM batteries. Their charge acceptance characteristics differ and they often require special charging requirements.
Type & size of charger
If you have an older charger that doesn’t allow the user to select between automotive, deep-cycle, AGM, etc., an upgrade is often needed to effectively charge different types of batteries. There are single-stage and multi-stage chargers with varying voltage regulation levels. Always choose the correct charger for the battery you are charging.
Voltage regulation of the charger
If you recharge deeply discharged batteries, you will need a charger that cuts off (regulates) at a higher level. For example, a 12-volt battery charger may need to charge at more than 15 volts for batteries deeply discharged while other batteries, only lightly discharged, may require just
In general, most consumer battery chargers sold today are single-stage ‘taper’ chargers. This means that the charger will react only to the battery’s internal resistance to change the current (in amps). These chargers typically cost less and have less electronics and sustained regulation levels. The charger may start at a high charge current level, but will taper down to a lower current to charge the battery slower. Just because the charger starts at a high level at first doesn’t keep it from slow-charging.
A more elaborate charger is a multi-stage charger that will allow a high constant current, a medium to slow and then a maintenance stage. These often cost more but charge more effectively.
Charging too slow = When you can’t recharge fully within 8-10 hours.
Charging too fast = Battery gets hot, typically when the charger’s output is greater than a third of battery’s amp-hour rating
How do I know how much to charge the battery? Is it better to charge longer?
The time needed to effectively recharge depends on the battery’s capacity and its state of charge. An auto starting battery’s ampere hour capacity can frequently be calculated by its reserve capacity multiplied by .6. Many other battery types require the manufacturer’s information.
The battery’s approximate state of charge should be tested only when the battery is static and hasn’t recently been discharged or recharged.
For more than 20 years, Gale Kimbrough has been the face of technical expertise for Interstate Batteries customers. Although he is retiring from Interstate Batteries to spend more time with his family, Mr. Battery will continue to make battery science interesting and fun for our readers. Got a question? Ask him at interstatebatteries.com/mrbattery.