Jim Davis said "A voltmeter doesn't give you quite the information of 
the ammeter," and seemed to feel that it doesn't offer the wealth of 
information that an amp meter does.  I've changed my mind over the years 
on that comparison.  The one thing that an amp meter does better than a 
volt meter is, clearly show just how "active" your battery(s) are/is.  An 
active battery (connected group of cells as recently well instructed) is 
able to accept and deliver current at a high rate.  Now if you have a 
pint sized motor (eg. VW) spinning it with the starting motor requires so 
little current compared with what's typically available with modern 
batteries, that even a tired bat near the grim recycling center, can spin 
it quite convincingly.  But when the motor starts, an active battery will 
briefly pull current like mad as it reestablishes it's ion balance.  As 
you watch an amp meter, the tired one accepts the recharge visibly 
slower.  So the amp meter's main claim to great utility lies in revealing 
battery condition, not that of the charging system.
  Now the volt meter offers a better pallet of information for the Westy 
owner.  First of all, the charging system's voltage is its best single 
indicator as to it's condition.  After a long cold cranking period or 
hours of motor-off coach electrics load, if it can't pull 13.8 volts very 
quickly against the load of a hungary active battery, you know it's not 
able to deliver the current it should.  So in this round about way, it 
reveals current delivery.  But there's more.  After a long parked 
motor-off coach electics drain period, you may have concerns as to having 
enough power left to restart in the morning.  Faced with killing the TV 
late at night while absored in the plot just to save the battery, 
restarting the motor to recharge for a bit while irritating your 
neighbors, or taking a chance, the amp meter is as instructive as your 
speedomenter.  But the volt meter tells you EXACTLY what percentage 
charge is left in your battery.  I don't have the chart before me, but 
it's often published.  The better photo cell energy books always include 
it.  My books on that topic are at another place of mine over a thousand 
miles away, so somebody please post this chart data showing voltage vs. 
percentage charge.
  I vote for the volt meter, no contest.
  How many of you have elected to run a second "coach" battery, isolated 
with the standard diode/heat sink package sold at RV centers?  Three 
potential locations are the two wells behind the front seats, and the 
large cavity to the right of the motor compartment.  I have an inverter 
ready to pop in, but it's wave shape has nasy vertical walls.  I didn't 
know that when I bought it, and running electronics with it may be a 
marginal case.  Any inverter equiped Westys?
  John