When I got the alarm system service required on the T5 - it turned out to be the siren...but when I pulled the siren (thank you Howard for the directions), the board was fried...not chemically, from a leaking battery, but it looked like it had really overheated. New siren, all was well...just be careful drilling out the rivets - easy to get them hot, then they melt the plastic and spin...
But I agree - the battery should be replaceable.
2006 Corolla (kid's car - 165K, Eco Contacts, Castrol Edge 5W30)
2005 MB S600 (84K, Michelin AS3, M1 0W40)
2002 V70-XC (201K, AltiMax RT43, Pennzoil Ultra 5W40)
2002 V70-T5 (179K, IPD bars, Bilsteins, Conti PureContact, Mobil 1 0W40)
1992 MB 300E (Sportline - 160K, Yokohama Avid, Castrol Edge 0W40)
1990 4-Runner (V6, 4WD, mild lift - 257K, 31" BFG AT KO, Castrol 10W40)
1932 Packard Sedan (straight 8, dual sidemount spares, original paint and interior, Shell Rotella 15W40)