I had a personal e-mail about this and can only say that a user can only go on reputation. Price may not be a good guide.
In my apprenticeship days, my boss at the time took me along to a battery manuf. nr. Leeds called "Doric Batteries". Most interesting. The 'plates' as they call them consist of a rectangular lead grid. One pole is left as it is, and the grid on the other is filled with a yellowish white lead oxide paste simply by pressing it in with a cloth by hand. It was impressed on me that it was important to press this paste well in, otherwise later on in the battery's life it would fall out. The pos. and neg. plates are separated by oak or glassfibre separators. The plastic cell walls and bottom of the battery case were organized so that any paste falling out would fall into a space in the acid at the bottom, hopefully not shorting out the cell. In those days the top of the battery of cells were visibly connected by thick lead connectors which were poured on in the hot molten state using a little mould for each. This led to a tip they gave me for to recognize a well-worn battery. The huge current flowing through the cell demanded by the starter motor would "twist" the plates very slightly out of line, so much so after a few years of use, peeping along the length of the side-top of the battery would reveal the alternate twist from cell to cell. This is of course the time that the paste falls out into the battery bottom. Batteries were tested by a "leg-tester", a long handled voltmeter with a heavy shunt resistor and a pair of spikes to dig into the lead connectors. The voltmeter would then show an open-circuit voltage until the user pressed a handle at the side inposing a 100 amp. current on it. You then judged by how far the voltage fell as to how good the battery was. There was the usual green=good part and red=bad. Here are a few facts about lead-acid batteries which may help.
In your 12volt (nominal) car battery, there are six cells at 2.2volt each.
When tested off-load and not being charged by the alternator, a good digital voltmeter will indicate 12.6 to 12.8volt for it.
When battery is being charged by the alternator (it's a constant-voltage charging system) the reading will be 14.4volt. It has been so on every car I've ever tested, and is incidentally a handy way of establishing that the alternator is charging as it should. This does not mean the battery is ok! It may be worn out even so.
The dilute sulphuric acid (electrolyte) in the battery does not evaporate, but the water content can. Top up with soft tap water, or de-ionized water (e.g. from a dehumidifier) if your local tapwater is hard with chalky minerals. These alkaline minerals will react with the acid diluting it. If the acid becomes diluted, the internal resistance rises, slowing the heavy current cranking speed. In very cold climates, the acid is stronger than usual on purpose. There are also jellybatteries where a neutral gel is used to carry the liquid dilute acid. Means no topping up, no spilling. WARNING! Never short a jellybattery, it will immediately knacker it.
When your battery says it is f'rinstance 100 ampere-hours, it does not mean it will supply a hundred amps. for an hour! The 100 ampere-hours capacity is at the 20 hour rate, meaning you have to take 20 hours to discharge it; then you get 100% of stored charge back. Take anymore current then the efficiency starts to drop so that in say, 10 hours it's only 50% or so. Never leave a lead-acid battery on it's own and uncharged for months on end; when you come to use it, it'll be no good. Keep it on a v. small trickle charge all the time, or an hour a week. If you can't, drain out the acid, keeping it separate (the "dry-charged" state).
If you're a bit short of the readies, you might be able to rejuvenate an old battery thusly:--
Ensure it's topped up.
Keeping it level, bang it up and down on the bench to dislodge any paste bridging the plates. This is a matter of guesswork as to how long.
Then trickle-charge it at a quarter amp. or so for a week or two.
You could well be surprized at the effect.
Finally, as I've mentioned, a computer controlled car (most now) needs a top quality battery.
Leedsman.