4. More RC (Reserve Capacity) or Amp Hours is a good thing.

Larger RC or Amp Hours is better because of the effects of increased parasitic (ignition key off) loads, normal battery self discharge while in long term parking or storage, and the demands of stop-and-go driving. Amp Hours (AH) is normally used to describe the capacity of deep cycle and international car batteries.

When comparing Amp Hour specifications, use the same discharge rates, expressed in hours. There is a relationship between the weight of the battery and the amount of RC or Amp Hours. A heavier battery has more lead and is normally better choice.

Batteries are generally sold by model or type, so the BCI Group Numbers can vary for the same price. This means that for the same price, you can potentially buy a larger battery with more RC or Amp Hours than the battery you are replacing.

For example, a 34/78 group might replace a smaller 26/70 group and give you an additional 30 minutes of Reserve Capacity. If you buy a physically larger battery, be sure that the replacement battery will fit, the cables will connect to the correct terminals, and that the terminals will NOT touch metal surfaces such as the hood when it is closed.

5. Batteries are perishable, so buy fresh.

Unless a battery has periodically been recharged, never buy a non-sealed wet Low Maintenance battery that is more than three months old or a sealed wet Maintenance Free battery that is more than six months old because they have started to sulfate.

"Dry charged" batteries are shipped without electrolyte, but usually have "sell by" dates of one to three years. Battery dealers will often place their fresher batteries in the rear of the rack or in a storage room. The date of manufacture is often stamped on the case or printed on a sticker. If you cannot determine the date code, ask the dealer or contact the manufacturer.

6. Look for longer free replacement warranties.

Battery replacement warranties are not necessarily indicative of the quality or cost over the life of the battery. Some dealers will prorate warranties based on the list price of the bad battery, so if a battery failed half way or more through its warranty period, buying a new battery outright might cost you less than paying the difference under a pro rated replacement warranty.

Long pro rated replacement warranties tend to be marketing gimmicks by some battery manufacturers, distributors or dealers to get you to continue buying their batteries. The exception is the free replacement warranty, which represents the risk that the manufacturer is willing to assume. A longer free replacement warranty period is better.