Gel batteries vs. wet cells vs....

May 1, 2011 | By Richard Prince


I own five vintage cars from 1934 through 1950 and have been able to apply many of your tips to my babies.

My question is in regard to 6-volt batteries as my cars are all in this category. Four are positive ground and one, the 1950, is negative ground. All five are

running original equipment starters, generators and voltage regulators which have all been rebuilt, and new wiring was installed during restoration. In one car I run a wet cell battery while in the other four I have elected to go with the Optima gel batteries because they seem to offer higher cold cranking amp ratings. The added CCA rating will subsequently give more enthusiastic cranking speeds and are much more forgiving of down time and longevity.

My question is in regard to the gel batteries compatibility with stock generators and voltage regulators. Some of my old car buddies think this is not a good combination and cite failures they have had, while others, like myself, seem to think it’s a better way to go.

The reason I ask is that I seem to get mixed readings from my amp meters in the four vehicles with gel batteries. Some seem to put heavy demands on the charge rates for extended periods of time while others fluctuate a great deal.

Perhaps this is the end result of age and who rebuilt what, but I would like your input to end the controversy.


Most gel batteries are essentially the same as conventional lead-acid batteries but in a gel battery a gelling agent such as silica is added to the electrolyte to transform it from a liquid into a gel. Gel batteries do have a number of weaknesses that must be addressed or premature failure will usually result. One of these is that gel batteries require a lower recharge voltage than their liquid electrolyte counterparts so in an automotive application the charging system should be modified accordingly.

But this is irrelevant for you because you state that you’ve installed an Optima gel battery and that is not really a gel battery. Instead, it relies on something called Absorbed Glass Matt (AGM) construction. This type of construction allows the electrolyte to be suspended in close proximity to the plate’s active material.

In other words, the electrolyte is held on glass mat separators by means of capillary action.

In the particular case of Optima, this company uses their own patented spiral wound method for configuring the cells in order to optimize each battery’s efficiency and, among other things, give each battery the benefit of very low internal resistance. The low internal resistance permits higher output and more efficient charging. At the same time, however, it changes the battery’s charging characteristics, particularly when it’s severely discharged. When the battery is charged above about 4.5 volts your vintage car’s charging system should behave normally but if the Optima battery discharges below about 4.5 volts the charging system may be too confused to charge it properly.

So, your best course of action is to not let the Optima batteries get severely discharged and if they do, use a modern charger with a setting for AGM batteries to recharge them.

As far as your observation that some of the cars with an Optima battery seem to be charging heavily for extended periods of time while the charging rate in the others fluctuates a great deal, I don’t think either situation is due to the unique characteristics of the Optima batteries you’ve installed. The conditions you see are most likely due to inaccurate gauges and/or erratic performance of the vehicles’ charging systems.