Batteries and Chargers

by Bryan A. Thompson

Last Updated 2/10/2003

Important!  When upgrading UPS storage batteries, use only use batteries and chargers marked "Trolling Motor" or "Deep Cycle" sealed lead-acid batteries.  Other batteries, such as car batteries, lawn and garden batteries and even Marine Starting batteries can't be fully discharged multiple times without being damaged, so don't use them.  I won't go into the details of how deep cycle batteries or chargers work or why they're better than car batteries for this application - I'm sure that information is available on the web somewhere.

 

Dry Cells

It's a good idea to have some of these stored in your car and home in case of an emergency in case you forgot to charge the rechargeables and for use until other emergency energy supplies are in place. 

They're not rechargeable, so I won't cover them here. 

 

NiCd Batteries

These have largely been replaced by NiMH and Lithium Ion rechargeable batteries, so I won't cover them here.

 

NiMH Batteries

These are cheap renewable sources for portable energy.  They store a lot more energy than NiCds did - about 3X as much.  They're like $1-$2 each at Walmart for AAA/AA/C/D sizes, and 9Vs are available.  You need a charger made specifically for NiMH batteries to prevent overcharging.  Nice ones are available at Radio Shack for about $25. 

These are great for powering AM/FM/FRS/Weather radios, LCD televisions, flashlights, some alarm systems, smoke alarms, CO detectors, digital cameras, etc. 

They can be partially charged by repeatedly heating and cooling them (within their recommended temperature range). 

Energy Capacity

Not much.  These are really intended to power portable devices and be charged from another power system such as a generator or UPS.  To calculate stored energy, multiply terminal voltage by current rating given by the manufacturer.  Typical results are 1.2V * 1600mAH = 1.92 Watt Hours per cell.  Remember that this can change depending on how quickly the energy is used and the battery temperature.

Cost to store this energy

About $3 per cell, so about $1.56 per Watt, plus the one-time cost of the charger. 

Storage Characteristics

Energy can be stored in NiMH batteries for a lot longer than in NiCds.  I have used some that I charged and stored for 6 months, and they appeared to have a close-to-full charge in them.

 

Lithium Ion Batteries

These are really lightweight rechargeable batteries and they require dedicated Lithium Ion chargers and are very expensive, but they aren't widely available, so I won't cover them in-depth here.  It might be worth it if you really needed to minimize weight, like in portable electronics, for backpacking, etc.

Energy Capacity

Not much.  These are really intended to power portable devices and be charged from another power system such as a generator or UPS.  To calculate stored energy, multiply terminal voltage by current rating given by the manufacturer.  Typical results are 1.2V * 4000mAH = 4.8 Watt Hours per cell.  Remember that this can change depending on how quickly the energy is used and the battery temperature.

Cost to store this Energy

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Storage Characteristics

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Sealed Lead Acid Batteries

Standard car batteries are great for providing instantaneous current for starting, but not great if you intend to fully discharge the battery, such as in a UPS application.  In an emergency, you can use the energy stored in your car battery to recharge cell phone batteries, but you shouldn't connect an inverter to one of these without the car running. 

Since they're not practical for other purposes, I won't cover them in-depth here.

 

Deep Cycle Sealed Lead Acid Batteries

These are also called Trolling Motor batteries.  They deliver lesser maximum current than car batteries for a lot longer period of time.  They can hold a lot of energy and are reasonably priced - I bought some 115A 12V (1.38KWH) batteries at Walmart for $55 each.  These are great for storing large amounts of energy produced by gasoline-powered generators, solar, wind- or hydro-electric generators.  The power stored in these can be converted to 120VAC with the use of an inverter / UPS. 

Energy Capacity

Typical sizes for a trolling motor battery are 12V at 115Amp Hours = 1.38 Kilowatt Hours.  Remember that this can change depending on how quickly the energy is used and the battery temperature.

Cost to store this energy

They cost $55, and I buy a battery box, fuse holder, connecting rings and a connector pair.  Total cost per battery is about $85.  This means it costs $61.5/KWH to store the electricity, plus the one-time cost of the charger.  Therefore you should consider alternate forms of energy storage for extended length emergencies.

Charging and Storage Characteristics

Energy cannot be stored indefinitely in these batteries.  They come from the factory fully charged.  A process called Sulfation starts after about 3 months without charging.  It is possible to get a charger that will maintain the charge on these batteries automatically for <$50.  I store mine connected to operating UPSes, which is essentially the same thing as a charger.  If you don't do this, they should be recharged with a deep-cycle battery charger once a month.

 

 

 

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