How long do battery backups last?

[prochobo 10+ year member]

I'm gonna be getting one of these modules, a DEI 520T to add on to a Viper 791xv that I just ordered from HCCAfan. Do they recharge? This hooks up to the brain and supplies power to all the horns from there right? I'm gonna get 2 horns under the hood and 2 piezos in the cabin, will this be enough to keep them going for a good long time?

http://cgi.ebay.com/DEI-520T-12V-Battery-Back-up-Power-Source-for-Car-Alarm_W0QQitemZ9731229968QQihZ008QQcategoryZ94833QQcmdZViewItem

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[project f-150 10+ year member]

It will last long enough to be effective. and yes they recharge!!