Battery powered device hardware design tips
You need to be certain on your voltage and current specifications.
You say 150 ma peak load.
If properly configured The LT1302-5 will easily meet your stated need. If it is failing to do so there is either something wrong with your circuit or your load is far greater than you state. The Digikey parametric selector suggests that there are 150 mA and 600 mA Iout versions but this does not appear to be suppoted by the datasheet.
The LT13o2-5 will provide up to 600 mA at 5V out. The graph below (from page 1 of the LT1302 data sheet shows that peak efficiency with vIN = 2v is achieved at Iload ~= 200 mA - above your stated requirement. and they show results up to Iout = 600 mA.
The battery current will be ~+ Iout x Vout/Vin x 1/Z
where Z = converter efficiency (0 &lt;= Z &lt;= 1).
For say 80% efficiency, 2V in and 5V out and 150 mA load, I battery
~= 150 mA x 5V/2V x 1/0.8 =~ 500 mA.
That is well within the capabilities of Alkaline AA cells or of rechargeable NimH cells.
Battery life at 150 mA ~= Battery_Capacity / Battery_Current x K
where K is a derating factor 0 ...1 which drops as load increases and as the battery is used (due to rising internal resistance).


4 x AA cells will provide 5V for only a small part of an Alkaline battery's life and not at all with NimH.
5V/4 = 1.25V
You need at least 1..25V/cell to regulate it down to 5V.
Alkaline and Nimh can be considered to be 'dead' at 1V.
So 5 cells and an LDO (low dropout regulator) would be a minimum.
Valkaline_new ~= 1.65V, so initially 5 cells would give you 1.65 x 5 = 8V +.