Parallel charging LiPo packs has become very common in the RC hobby. Granted, there is not a lot of empirical evidence about how good or bad this is. Only the fact is that a lot of people do this on a daily basis.
Personally I have been parallel charging 6s LiPo packs for 2 years now with good results. I have some budget packs that are over 100 cycles, so in that regard, I am happy with the life I got out of the pack.
My parallel charging routine was not very stringent. I likely never charged packs with over a 0.25V/cell difference during this time. I think in the future I will be more careful about the voltage of the packs. My recommendation would be to stay under 0.1V/cell difference.
The problem with parallel charging is that it is quiet easy to make a mistake, and connect packs of dissimilar voltages. So if you are going to do this, I would always double check your pack voltages before connecting.
A very good resource on parallel charging can be found on the Tjin Tech site. This is a very thorough examination IMO. If you scroll to the bottom it also addresses the potential surge currents when connecting the packs, and also includes experimental measurement of current that is released at the initial connection.
See Smart charging circuit for NiMH battery pack where the answer states
In such cases a very reasonable charging strategy is to terminate
charge at 1.45V per cell.
It is reasonable to believe he is referring to "at the cell".
It is worth noting that BQ2002PN is a FAST charge. You need to ensure it will not burn out your Cells. A good charger will switch between slow and fast. In-circuit application charging should design the charge rate to exceed the discharge rate of the applications load and consider the margins. It is more then acceptable to use a fixed supply voltage and resistance to supply a minimal charge rate. Assuming it is not too high, a small trickle small enough not to exceed self heating, works.
Before Low Self Discharge Cells we made a +12V with Diode drop and Resistor to slow charger for a dozen parallel Cells, (i.e "Hot and Ready", not really hot). It is cheaper than a smart charger. And we could keep the charge rate very low. Lower then most chargers slow rate as they are still higher (enough for larger capacities) than needed and wasteful.
In fact I have several Maha and LaCrosse (nice chargers) for NiMH, but they are too smart. When using more than one cell, on a load, in series (typical 3 and higher) they UN-evenly discharge. Where one gets below the Under Voltage sense and considers it a failed cell. But putting it on a 5ma source for a minute kicks it up and then it works on the Smart Chargers.
You should refer Ada's page on Minty Boost. LiPo's are the in spot for in circuit charging and plenty of chargers for them. Such as SFE's Lipo Charge Boost. There are plenty of examples out there.
Best Answer
Summary:
There are better newer ICs to use.
This IC will damage newer high capacity NiMH cells (see below)
Note that the page that you referenced said
"All versions are Not Recommended for New Designs."
I was going to say that it would be an OK charger IC BUT a look at the MAX712/713 datasheet shows that the IC is now dangerous junk and should not be used to charge modern higher capacity NiMH cells (such as Sanyo Enelooop batteries).
The problem is that the IC is always in only one of two states - fast charge or trickle charge. Whereas older lower capacity NiMH cells could be safely trickle charged, newer higher capacity one MUST NOT be trickle charged. This is because the structures and chemical present in older cells which allows recombination of Hydrogen gas formed at end of charge cycle is not present in modern cells - as the manufacturers have 'stolen' the space to make room for additional active material.
I looked at as many manufacturer's recommendations as I could find in recent years and none of them 'allowed' trickle charging in the time honoured sense (For NiCd this might have been as high as C/10 indefinitely). Some manufacturers "allow" a very low post charge trickle charge rate for a very short time or in one case an exceptionally low ongoing rate (C/1000?) but this is not the norm.
The change from OK to forbidden tends to be capacity based and will vary by manufacturer but, as a very rough guide, an AA cell of <= 1600 mAh capacity when this was "leading edge" still allowed trickle charging. However, now that manufacturers have become accustomed to making cells which are averse to trickle charging, even if they make a low capacity 'budget' cell, there is no certainty that they will re-equip the lower capacity cells with the ability to be trickle charged.
While it is not 103% certain where Eneloops stand in this matter, it is exceedingly unlikely that trickle charging them is a good idea, and their ultra-low self discharge rates (years) means it is not necessary.
There are better newer ICs to use. Note that the page that you referenced said
"All versions are Not Recommended for New Designs."