Mobil Phone Charging:
Manufacturers claim that you should only use their chargers.

Philipson says: Nokia told me that most phones sold in the past few years will work with the ACP8A and ACP12A 5.7-volt chargers.

"Unauthorized Charger" Message on Razr:
The motorola Razr may give you an "unauthorized charger" message with third party chargers.

The USB specification limits the minimum power available from the interface voltage pins to 500 mA at 5 volts, or 2.5 W. The GSM version of the RAZR, which first adopted the USB charger cable, can apparently live with that, but the CDMA phone is more power hungry and needs more than 2.5W to charge. The chargers supplied by Motorola will deliver significantly more than 500 mA, and as a practical matter a lot of other USB chargers and interfaces will too, but with the latter you can't count on them to support more than the standard requires.

It may or may not still charge the phone, you'll have to try it to see. If it does charge the phone it will take longer to do so than a higher power charger would.
Source: Dennis Ferguson at www.wirelessforums.org

Another person said "I'm not sure that's all there is. My wife has a V3c, and I tried a Zip-Linq USB power supply rated 5V @ 1000 mA and got the same error message."

Had similar experiences with another phone and just kept exchanging them at Wal-Mart until one worked. Cables:
USB Mobil Phone Charge Cables
how-to make a usb battery

Voltages:
Some devices can run from substantially higher voltages than the rating of their standard plugpack. This lets them deal with unregulated plugpacks whose voltage only drops to the rated figure when the plugpack's delivering maximum current. Don't bet on any particular gadget being able to do this, though. If you over-stress a regulator, it can easily overheat and die.
Source: USB Mobil Phone Charge Cables

Charging 12 V backup batteries:
Most 12V gell cells can be charged at 13.8 V to their long term (eg. standby power mode) capacity. However, 14.2 - 14.5 will get you full charge.

Most Gell Cell battery experts would probably tell you 13.6 V is about optimum for float charging a Lead Acid gell cell. Going to 14V or higher tends to shorten their lifespan by warming them excessively so that they "dry out" more quickly.

From a 13.8 V supply place a 10 -30 ohm 10 Watt resistor in series with the supply and battery. Do make sure with a voltmeter across the resistor (remember I = E/R) that the charging current does not exceed 10% of the rated battery capacity (eg 10AH would be 1 Amp charge). Leave on the supply until the current goes to .010 amp. or so... A very cheap way to do this. Also, do fuse the line between the battery and the supply (try a fuse equal to the battery capacity (10AH = 10 amps).
Source: www.eham.net/forums/EmergencyCommunications

Sample charging requirements:

Mobil Phones - radios
Motorola V330         5.9V 375 mA
Motorola RAZR V3c     5 V  500 mA
Plantronics Headphone 5 V  180 mA
Kenwood HandiTalkie  13.8 V 650 mA

Laptops
Apple PowerBook G4 24 V 1.9 A
Toshiba Portoge    15 V 2 A
Other Computer:
Card Reader HD      5 V 800 mA
LaCie Firewire     12 V
Canon PIXMA iP90 printer  16 V 1.8 A

Firewire 7-30 V

Other:
Canon ZR90 digital camcorder 8.4 V 1.5 A
Magellan eXplorist 500 GPS   5   V 1 A
Sony CD MP3 player           4.5 V 500 mA

USB battery power packs:
www.ladyada.net/make/mintyboost/make.html
www.usbgeek.com/prod_detail.php?prod_id=0347