I wouldn't run this drop-in with alkalines if I could help it. I would run this with rechargables or lithium primaries. [Edit]Sorry, current draw at 6v is 1800mA. I don't know if alkalines will be able to do that. Another thing that sticks in my mind is that this drop-in drops out of regulation at 5v. That's just 1v under the starting voltage of 4 alkalines. Another reason to use rechargables or lithium primaries.I have been considering purchasing the P7 drop-in that Gene offers but I was wondering what the approximate runtime would be in a standard 4-D maglite. I am planning to use standard batteries nothing rechargeable. Thanks.