A little light reading. Don't have any ties to these folks but the info seems resonabley complete, clear and good.
I have L-16's and a place to put them, however at 124lbs and 16+" tall, I would not wish them on anyone that did not require very high capacity. I have found 4V cells (24" tall) at several 'off the grid' places on the web. Any of those folks that specialized in 'OFF THE GRID' solar/wind etc are a wealth of info on things battery.
Excerpted from:
http://www.windsun.com/Batteries/Bat...attery%20Types
Lifespan of Batteries
The lifespan of a battery will vary considerably with how it is used, how it is maintained and charged, temperature, and other factors. In extreme cases, it can vary to extremes - we have seen L-16's killed in less than a year by severe overcharging, and we have a large set of surplus telephone batteries that sees only occasional (5-10 times per year) heavy service that are now over 25 years old. We have seen gelled cells destroyed in one day when overcharged with a large automotive charger. We have seen golf cart batteries destroyed without ever being used in less than a year because they were left sitting in a hot garage without being charged. Even the so-called "dry charged" (where you add acid when you need them) have a shelf life of at most 18 months, as they are not totally dry (actually, a few are, but hard to find, the vast majority are shipped with damp plates).
These are some general (minimum - maximum) typical expectations for batteries if used in deep cycle service:
Starting: 3-12 months
Marine: 1-6 years
Golf cart: 2-6 years
AGM deep cycle: 4-7 years
Gelled deep cycle: 2-5 years
Deep cycle (L-16 type etc): 4-8 years
Rolls-Surrette premium deep cycle: 7-15 years
Industrial deep cycle (Crown and Rolls 4KS series): 10-20+ years
Telephone (float): 1-20 years. These are usually special purpose "float service", but often appear on the surplus market as "deep cycle". They can vary considerably, depending on age, usage, care, and type.
NiFe (alkaline): 3-25 years
NiCad: 1-20 years
Battery Size Codes
Batteries come in all different sizes. Many have "group" sizes, which is based upon the physical size and terminal placement. It is NOT a measure of battery capacity. Typical BCI codes are group U1, 24, 27, and 31. Industrial batteries are usually designated by a part number such as "FS" for floor sweeper, or "GC" for golf cart. Many batteries follow no particular code, and are just manufacturers part numbers. Other standard size codes are 4D & 8D, large industrial batteries, commonly used in solar electric systems.
Some common battery size codes used are: (ratings are approximate)
U1..................34 to 40 Amp hours......12 volts
Group 24..........70-85 Amp hours.........12 volts
Group 27..........85-105 Amp hours.......12 volts
Group 31..........95-125 Amp hours.......12 volts
4-D................180-215 Amp hours.......12 volts
8-D................225-255 Amp hours.......12 volts
Golf cart & T-105.......180 to 220 Amp hours.........6 volts
L-16.........................340 to 415 Amp hours........6 volts
Cycles vs Life
A battery "cycle" is one complete discharge and recharge cycle. It is usually considered to be discharging from 100% to 20%, and then back to 100%. However, there are often ratings for other depth of discharge cycles, the most common ones are 10%, 20%, and 50%. You have to be careful when looking at ratings that list how many cycles a battery is rated for unless it also states how far down it is being discharged. For example, one of the widely advertised telephone type (float service) batteries have been advertised as having a 20-year life. If you look at the fine print, it has that rating only at 5% DOD - it is much less when used in an application where they are cycled deeper on a regular basis. Those same batteries are rated at less than 5 years if cycled to 50%. For example, most golf cart batteries are rated for about 550 cycles to 50% discharge - which equates to about 2 years.
How depth of discharge affects cycle life on batteriesBattery life is directly related to how deep the battery is cycled each time. If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD. If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%. Obviously, there are some practical limitations on this - you don't usually want to have a 5 ton pile of batteries sitting there just to reduce the DOD. The most practical number to use is 50% DOD on a regular basis. This does NOT mean you cannot go to 80% once in a while. It's just that when designing a system when you have some idea of the loads, you should figure on an average DOD of around 50% for the best storage vs cost factor. Also, there is an upper limit - a battery that is continually cycled 5% or less will usually not last as long as one cycled down 10%. This happens because at very shallow cycles, the Lead Dioxide tends to build up in clumps on the the positive plates rather in an even film.
The graph above shows how lifespan is affected by depth of discharge. The chart is for a Concorde Lifeline battery, but all lead-acid batteries will be similar in the shape of the curve, although the number of cycles will vary.
Amp-Hour Capacity
All deep cycle batteries are rated in amp-hours. An amp-hour is one amp for one hour, or 10 amps for 1/10 of an hour and so forth. It is amps x hours. If you have something that pulls 20 amps, and you use it for 20 minutes, then the amp-hours used would be 20 (amps) x .333 (hours), or 6.67 AH. The accepted AH rating time period for batteries used in solar electric and backup power systems (and for nearly all deep cycle batteries) is the "20 hour rate". This means that it is discharged down to 10.5 volts over a 20 hour period while the total actual amp-hours it supplies is measured. Sometimes ratings at the 6 hour rate and 100 hour rate are also given for comparison and for different applications. The 6-hour rate is often used for industrial batteries, as that is a typical daily duty cycle. Sometimes the 100 hour rate is given just to make the battery look better than it really is, but it is also useful for figuring battery capacity for long-term backup amp-hour requirements.
Why amp-hours are specified at a particular rate:
Because of something called the Peukert Effect. The Peukert value is directly related to the internal resistance of the battery. The higher the internal resistance, the higher the losses while charging and discharging, especially at higher currents. This means that the faster a battery is used (discharged), the LOWER the AH capacity. Conversely, if it is drained slower, the AH capacity is higher. This is important because some folks have chosen to rate their batteries at the 100 hour rate - which makes them look a lot better than they really are. Here are some typical battery capacities from the manufacturers data sheets:
Battery Type.............100 hour rate..........20 hour rate.......8
Trojan T-105................250 AH...................225 AH.........n/a
US Battery 2200..............n/a......................225 AH........181 AH
Concorde PVX-6220.......255 AH...................221 AH.........183 AH
Surrette S-460 (L-16)....429 AH...................344 AH.........282 AH
Trojan L-16..................400 AH...................360 AH...........n/a
Surrette CS-25-PS........974 AH...................779 AH..........639 AH
State of Charge
Here are no-load typical voltages vs state of charge
(figured at 10.5 volts = fully discharged, and 77 degrees F). Voltages are for a 12 volt battery system. For 24 volt systems multiply by 2, for 48 volt system, multiply by 4. VPC is the volts per individual cell - if you measure more than a .2 volt difference between each cell, you need to equalize, or your batteries are going bad, or they may be sulfated. These voltages are for batteries that have been at rest for 3 hours or more. Batteries that are being charged will be higher - the voltages while under charge will not tell you anything, you have to let the battery sit for a while. For longest life, batteries should stay in the green zone. Occasional dips into the yellow are not harmful, but continual discharges to those levels will shorten battery life considerably. It is important to realize that voltage measurements are only approximate. The best determination is to measure the specific gravity, but in many batteries this is difficult or impossible. Note the large voltage drop in the last 10%.
State of Charge........12 Volt battery............Volts per Cell
100%.............................12.7............. ............2.12
90%...............................12.5............ .............2.08
80%...............................12.42........... ............2.07
70%...............................12.32........... ............2.05
60%...............................12.20........... ............2.03
50%...............................12.06........... ............2.01
40%...............................11.9............ .............1.98
30%...............................11.75........... ............1.96
20%...............................11.58........... ............1.93
10%...............................11.31........... ............1.89
0...................................10.5.......... .............. 1.75
********* end of excerpt ********
http://www.windsun.com/Batteries/Bat...attery%20Types
Making Amps
Assumptions: 
Solar Amps:
Panel Array:
Linear Mode
