Might be worth trying rechargeable alkalines. They're pretty inexpensive (around 2x the cost of a standard alkaline plus £10/$15 for a special charger) and not too easy to come by, but they do deliver a true 1.5v and have an excellent shelf life (in fact, they arrive fully charged in their blister pack). They have the additional property of working better when only partially discharged before being recharged so ought to be suitable for immediate post-flight recharging.