Wow 250 beer tokens for a non-stop/start battery no way....
+1 on getting a new battery before trying to fault find any codes,
your 2007 battery will not last many more days and is telling you in advance before you get proper stuck at the most inoperative time.
I have got and recommend ( along with others on here) getting the Bosch S4 for about £85, check this thread here:
https://www.lexusownersclub.co.uk/forum/topic/107731-best-12v-battery-for-is250/
Note the bit about on-line retailer sites search boxes not coming back with this Bosch but I and others can assure it does fit, snug, but it does fit!
paul m.
ps you will not be able to get a Panasonic battery anymore :(