> What kind of current drain are you expecting from the 12v SLA
> battery?  P channels MOSFETs can be had with pretty reasonable
> specs these days, and it makes things a simpler if you can avoid
> voltage doublers

About 25W user power from the switchers, which are ~85%
efficient in theory -> 30W (2.2A) input @ 13.5V. The IRF5800TR,
a HEXFET/MOSFET, from RS caught my eye, which has a 4A rating
and is very cheap too, just NZ$0.68 (price not a major consideration,
although this is for a prototype and has to be "a" consideration), several
4A - 6A under NZ$3 and 10A for a $-ish more

http://www.datasheetcatalog.com/datasheets_pdf/I/R/F/5/IRF5800.shtml

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