Battery Maintenance
Some basic information for charging LA (Lead Acid) and SLA (Sealed Lead Acid) batteries.
LA batteries are widely used as starter batteries for all kinds of engines. A starter battery can supply large currents for short period's without damage. After use, they expect to be charged back to capacity as soon as possible and they can also be charged at high initial currents. They do however have to be charged with a voltage regulated charger. The high initial current drawed from the battery charger (or alternator) will drop off to a current regulated by the battery itself once the maximum charger voltage is reached. The charge voltage for LA batteries is 13.8 to 14V. If this voltage is exceeded then the battery will begin gassing and it's capacity will begin to destroy. You cannot pump more energy into a battery than it's full capacity specified.
Never leave a LA battery on a cold tile floor or on cement. Always leave it on wood or rubber or any material that is thermally non conductive like a cardboard box. I believe a LA battery has a 'body' temperature similar to your own. If left ie. on a tile floor then hypothermia will kill your battery in a few days and you will have to throw it away.
LA batteries discharge over time by themselves, so you have to charge them say once a month to maintain capacity. Leaving the battery unattended for a long period of time will result in sulfation which starts as soon as the battery begins to loses it's capacity and the battery will become useless. Sulfation is a crystal that forms on the plates of a depleted battery and it has an isolation effect between the plates.
One note of caution. LA batteries produces hydrogen as a result of the charge and discharge process. Do not expose to a flame or sparks, the hydrogen is super blamable and usually result in an explosion.
The LA batteries uses sulphuric acid diluted with distilled water to conduct electricity between the plates. If the battery is tilted the acid will run out. It will burn eyes, skin and destroy clothing and damage materials it comes into contact with. These batteries needs to be upright all the time. Wash with water asap.
Never test a LA battery like they did in the movies by drawing an arc with a piece of wire. Beside the risk of explosion from the hydrogen, there is a risk that the wire could weld itself to the battery poles and you will have a nice heat source that depletes your battery very quickly, damage the poles and creates a risk of fire. Invest in a volt meter, it is worth it.
Keep the acid solution covering the plates. Exposed plates cannot work. A part empty cell could destroy if too much current is drawed for the small wetted area to properly conduct. The acid never evaporates, but the distilled water does. Refill only with distilled water, tap water have mineral salts amongst other ingredients that can be harmful to the battery.
You also get LA batteries that is called leisure or deep cycle batteries. While most of the above applies, note that it is designed to produce less current at a time but can produce the lower power over a long period of time. Starter batteries do not like that. It is always desirable to charge a battery back to capacity as soon as possible after it was used. A 24 hour charge is enough, do not leave the battery on the charger over prolonged periods.
For marine applications use a maintenance free LA starter battery.
Please note that the new calcium batteries sold as car batteries is a different technology. Some new owners are experiencing in car charging problems since the calcium battery apparently requires a higher charging voltage than the standard LA batteries.
SLA (Sealed Lead Acid) batteries are of the same family as LA (Lead Acid) batteries, except for a few vital issues. Mostly these batteries are not understood in their charging requirements and is often discarded due to malpractice as a result of lack of knowledge. SLA batteries are stunning little buggers if you treat them properly and give years and years of good service. Personally I would always choose the SLA battery over LA batteries, except in the case of a starter application.
SLA batteries are used for powering a large variety of appliances and is favorable to use for back up power. They require no other maintenance other than charging and can be tilted upside down without acid spills. An ideal battery to use in a boat where tilting or even capsize will retain the acid inside. These batteries are also constructed with multiple protection layers, and the chances of them breaking in case of a drop or other physical force is very small. Their casings are really tough. Physical abuse will of course damage the battery internally.
The SLA batteries require 14.6 to 15V to charge properly. In addition to their charge voltage being higher than that of a LA battery, the current needs to be regulated as well. A 7Ah SLA battery for instance requires a max of 2.1Amp of charge current, the 105Ah batteries I have for the boat has a 10A charge limit. This means you cannot charge them directly from the car alternator or from the LA charger in the garage. You are almost certain to damage the battery with initial over current, and since the SLA requires a higher charge voltage, the car alternator can never charge it to full capacity. The lower working voltage of the car will instead keep the SLA battery in a semi depleted state. You can charge these batteries at a lower than specified maximum current, it will only take a bit longer. SLA batteries charge up faster than LA batteries does. They are also less susceptible to damage in the case of a deeper discharge.
SLA batteries requires a charger that limits charge voltage , and current limit it's charge for a specific size battery. The advantages of these batteries however more than make up for the additional charger requirements.
The following applies to LA and SLA batteries, although note that this may vary from manufacturer to manufacturer and the type of battery. This may however help you see why a battery lives longer if you charge it up directly after use instead of using it until it is depleted.
The graph represents a typical discharge vs service life for LA as well as SLA batteries.
Something else to note - When power is drawed off a battery by an appliance that requires a relative large current, ie an inverter to power a microwave, the battery may not be able to supply it's full rated capacity. A battery 100Ah, at 50A will not be able to supply the inverter for two hours, it will fall short.
A 12V LED light drawing 0.2A from a 7Ah battery may work longer than 35 hours, hence exceeding the battery's capacity. This would implicate that you should choose a battery size that can comfortably power the appliance you want to run off it.
LA and SLA batteries like to be worked. They like to supply power and expect to be charged right back again. If you keep them busy, they live a long time. From experience the SLA batteries last about 5 to 7 years, depending how well they are looked after and how badly you abuse them. You know how long your car battery lasts.
In the case of a permanently connected charger, the charger should ideally charge the battery up to voltage limit. Once the max voltage is reached, ie 14.7V, the charger should disconnect and allow the battery voltage to drop to below 13.4V to give the battery a rest in between. The charger in this case can be a small one, it needs to keep the battery in good charged condition over long periods of time.
Note that our battery driven lighting does not provide for low battery cut off. The reason is simply that if you are in an emergency situation, the battery cycle life is of less importance than the extra time you may need from the battery.