An electrical problem that doesn't let your car start and leaves you stuck in a parking lot or some place away from the fix that's needed is an unwanted problem we all do our best to avoid. So what can you do to lessen the possibility of a possible unwanted situation that involves an electrical system crash in your vehicle?
First of all make sure you spend double the money on a good car battery. A lead acid battery can cost between $75 to $125 dollars. The only reason liquid lead acid batteries are the most commonplace is liquid lead acid batteries were first developed in 1859 and they are the least expensive in today's world of automotive engine starting sources. In 1971 the sealed liquid lead acid battery was created that made it maintenance friendly.
VRLA (valve regulated lead acid) batteries include gel and absorbed glass mate which are not liquid. Gel batteries are as the name applies which is a "Gel". AGM batteries are silicate glass fibers mixed with boron and formed into a mat that holds the electrolyte. Non liquid gel batteries were created in the late 1920's and lead to the creation of the "Absorbed Glass Mat" batteries in 1957. The AGM (absorbed glass mat) battery was put into production in 1972 but mostly used for military applications and non vehicle applications like boats, motor homes, motorcycles and electronics. Nowadays you see more AGM batteries becoming available for use in production cars. AGM (absorbed glass mat) batteries can cost from $160 to $250 but have more advantages over liquid lead acid batteries.
AGM batteries are basically used in applications where the use of the vehicle is only used now and again as in boats and recreational vehicles. The non use discharge rate is much lower in non use applications than liquid lead acid batteries. The charge rate is much faster also. Some automotive manufacturers are installing AGM batteries as their standard new car power source because of today's higher vehicle power consumption. BMW right now is known to be the first to install AGM batteries in their 2007 models because of computer functions and braking.
AGM batteries are much better than liquid lead acid batteries but the downside of AGM batteries is you don't overcharge them. They will charge faster with a normal output alternator up to 14.5 volts and a high output alternator is not needed. When an AGM battery is used in a non use vehicle a solar panel is recommended with a trickle charge. AGM batteries will go bad if charged over 14.5 volts. Most problems with charging AGM's are in sports vehicles due to the rough environment they are used in. Toss away your old plug in garage battery charger and get a new one that maintains "Voltage" instead of amps. An AGM battery charger will sense a very low voltage in the battery and will start the recharge whereas an old charger does not sense low voltage and will not charge the battery.
These batteries are used in military vehicles that sit in storage for many years and start up after years in storage with no problem. I've read stories online where people have left their AGM batteries sitting in their garage for many years and they have retained their full charge. I use AGM batteries in my vehicles and disconnect the negative cable in the one that I don't use that often anymore and it starts right up when I run the engine occasionally. I've read complaints about the AGM failing often but that's only because of bad practices with them or using them in systems where the charging exceeds the recommended level. You can leave these batteries sitting for long periods of time without charging them but it's recommended that a solar panel with an extremely low trickle charge be used when not in use. Again I will say from my own experiences is to disconnect the negative cable to the battery when not in use.
The AGM vs Gel and the wet cell? The AGM has thicker plates that tend to not warp that easily during deep discharges and resist sulfur buildup's that destroy a wet cell battery. Wet cell batteries usually go bad after 4 years if they make it that length of time. The life expectancy of the AGM battery can be up to 10 years if not overcharged. Gel cell batteries are great for sports vehicles but tend to charge slower.
The Winner Is, "Absorbed Glass Mat" if you learn how to take care of them properly.
Here's a great article on on recharging an AGM battery