CPAP Backup

Re: CPAP Backup

And yes, you are looking at batteries aging out (used or not) and needing replace in 3-8 years or so... More expensive batteries can last longer. "Reduced Maintenance" batteries (like AGM), may not last quite as long--But if somebody does not check the electrolyte level in a flooded cell battery (less expensive type deep cycle battery), they will not last more than 6 months to a year anyway.

Here is a Battery FAQ--I suggest you read it and understand some of the issues. After you are done reading--you will wonder why anyone uses batteries in the first place--But, if batteries are taken care of--they will give very reasonable service for 5-8+ years.

Deep Cycle Battery FAQ

[h=2]Lifespan of Batteries[/h] The lifespan of a deep cycle 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 18 months at most. They are not totally dry - they are actually filled with acid, the plates formed and charged, then the acid is dumped out.
These are some typical (minimum - maximum) typical expectations for batteries if used in deep cycle service. There are so many variables, such as depth of discharge, maintenance, temperature, how often and how deep cycled, etc. that it is almost impossible to give a fixed number.

• Starting: 3-12 months
• Marine: 1-6 years
• Golf cart: 2-7 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): 2-20 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): 5-35 years
• NiCad: 1-20 years

I bolded the battery types you probably would be purchasing for this application. And you will find that there is a 2-4x difference in price for many of these batteries... I.e., a battery that lasts 15 years may cost 4x the price of a battery that lasts 4-8 years... And AGM "maintenance free" deep cycle batteries are 2x or more than the flooded cell versions (need to check electrolyte every month or two--and keep battery tops clean). Is that worth it?

The reason we want to know how much power is needed--Is because these components are not cheap and have a limited life (even the inverters/charge controllers/electronics will probably need to be replaced after 10 years of age). If you look at electronics these days--10 years is ~4-5 produce development cycles. Even if you could repair your laptop computer (getting parts and service support is almost impossible), would you dump a $1,000 repairing a laptop that has 1/10th the computing speed, memory, and 1/100th the disc space... Probably not.

And while much of these items have never been cheaper (solar panels, charge controllers, inverters)--They still have a limited life and a cost of replacement.

-bill